Migrate protected branch access levels to match constants in `Gitlab::Access`

Closes #20606 

Context: https://gitlab.com/gitlab-org/gitlab-ce/issues/20606#note_13561628

See merge request !5658

Fix `#down` for two protected branches-related migrations.

- The migrations called `add_column_with_default` with a `null` option, which the Rails `add_column` method accepts. This fails because `add_column_with_default` expects an `allow_null` option instead.

- The migrations have been fixed to use `allow_null`.

See merge request !5660

Refactor build artifacts documentation

## What does this MR do?

- Split user and admin documentation
- Use new location paths
- Add new Continuous Integration guide for the Admin area
- Link to new guide from the Admin area

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/20612

See merge request !5662

Signed-off-by: Rémy Coutable <remy@rymai.me>

Improve CI fixtures

cc @ayufan 

See merge request !5645

Merge branch '20512-fix-rename-add-users-into-project-to-add-users-to-project-and-projects-ids-to-project-ids' into 'master'

Fix Rename `add_users_into_project` and `projects_ids`

## What does this MR do?
Only modifies the name of a method that leaves more semantic and expressive and the name of the keywords arguments to the rails convention.

## Are there points in the code the reviewer needs to double check?
Only if it has been changed at every point that is calling this method and that passing arguments.

## Why was this MR needed?
To make the code more expressive.

## What are the relevant issue numbers?
Closes #20512.

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5659

Don’t close issues on original project

Closes #20527 -> https://gitlab.com/gitlab-org/gitlab-ce/issues/20527

See merge request !1981

Fix Import/Export not working in HA mode

Use a shared path instead of `Tempfile` default `/tmp` so the import file is accessible by any GitLab instance.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/20506

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5618

We never add things `into` projects, we just add them `to` projects. So how about we rename this to `add_users_to_project`.

Rename `projects_ids` to `project_ids` by following the convention of rails.

Update docs for CoffeeScript -> JavaScript.

## What does this MR do?
Removes some CoffeeScript docs and adds more JS ones

## Are there points in the code the reviewer needs to double check?
No

## Why was this MR needed?
To migrate some docs

## What are the relevant issue numbers?
#20098

## Screenshots (if relevant)
None

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5433

Merge branch '20491-remove-unnecessary-index_projects_on_builds_enabled-index-from-the-projects-table' into 'master'

Remove unnecessary index_projects_on_builds_enabled index from the projects table

See merge request !5611

Fix Devise deprecation warnings by updating omniauth provider paths to
use the new Devise/Rails 5 format.

See merge request !5331

Signed-off-by: Paco Guzman <pacoguzmanp@gmail.com>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Instrument Gitlab::Highlight

## What does this MR do?

This instruments the class `Gitlab::Highlight`.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

This class is not instrumented.

## What are the relevant issue numbers?

#18592

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5644

Fix confusing description of a blocked user.

## What does this MR do?
Rewrite confusing description of a blocked user in admin settings. If someone is blocked, the same message is displayed as if he is unblocked.

## Are there points in the code the reviewer needs to double check?
No.

## Why was this MR needed?
Because it seems that this is a cosmetic bug.

## What are the relevant issue numbers?
None.

## Screenshots (if relevant)
![blocked_user](/uploads/0782a82760ae19661d69c63a97daaf33/blocked_user.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5582

Improve performance of SyntaxHighlightFilter

## What does this MR do?

This MR improves the performance of `Banzai::Filter::SyntaxHighlightFilter`. See e9bacc6575d0002c6cab620075dea3dc7f93f100 for more information.

## Are there points in the code the reviewer needs to double check?

Styling mostly.

## Why was this MR needed?

Syntax highlighting is rather slow.

## What are the relevant issue numbers?

#18592 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [x] ~~API support added~~
- Tests
  - [x] ~~Added for this feature/bug~~
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5643

Fix Import/Export error checking versions

Fixes small bug preventing the correct error message about Import/Export version being displayed.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/20536

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5638

Improve AutolinkFilter#text_parse performance

## What does this MR do?

This MR improves the performance of `AutolinkFilter#text_parse` by using XPath queries for filtering out most text nodes.

## Are there points in the code the reviewer needs to double check?

Mostly the styling of things.

## Why was this MR needed?

Parsing text nodes is slow, mostly because most of this happens in Ruby.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/18593

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [x] ~~API support added~~
- Tests
  - [x] ~~Added for this feature/bug~~
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5629

- Split user and admin documentation
- Use new location paths
- Add new Continuous Integration guide for the Admin area
- Link to new guide from the Admin area

Remove unused images

## What does this MR do?
Remove unused images

```
bg-header.png
bg_fallback.png
chosen-sprite.png
diff_note_add.png
icon-search.png
icon_sprite.png
images.png
move.png
progress_bar.gif
slider_handles.png
```

## Are there points in the code the reviewer needs to double check?
Just need to check if the images are still being used 😄

## Why was this MR needed?
To reduce the technical debt of the project

## What are the relevant issue numbers?
Closes #20499 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5601

Fix Mystery Guest

## What does this MR do?
Makes the name of the local variable more expressive rather than using a character, which is the problem of the magic variable/mystery guest.

## Are there points in the code the reviewer needs to double check?
Only the partial that receives the new name of the local variable is being called.

## Why was this MR needed?
Ensure that the pass of local variable don't use a magic name.

## What are the relevant issue numbers?
Closes #20510.

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5657

Don't setup DB for slack notification build

## What does this MR do?
Fix error with build related to slack notification: https://gitlab.com/gitlab-org/gitlab-ee/builds/2834026

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## What are the relevant issue numbers?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5661

- The migrations called `add_column_with_default` with a `null` option,
  which the Rails `add_column` method accepts. This fails because
  `add_column_with_default` expects an `allow_null` option instead.

- The migrations have been fixed to use `allow_null`.

- In the final round of review (!5081), we moved the protected branch
  access levels from Rails enums to constants from Gitlab::Access.

- The migrations that moved us from the old data model (a single
  protected_branches table with developers_can_push and
  developers_can_merge flags) to the new one (separate tables for
  push_access_levels and merge_access_levels) was not updated.

- These migrations still used 0 to mean "Masters" and 1 to mean
  "Developers" (matching the previous Rails enum), while Gitlab::Access
  uses 40 and 30 for these, respectively.

- Once the migrations run, our data gets into a broken state.

- We fix this by migrating all `0`s to `40` and all `1`s to `30`.

- https://gitlab.com/gitlab-org/gitlab-ce/issues/20606#note_13561628

= Caveats =

- In Gitlab::Access, 0 represents NO_ACCESS. When we run this migration,
  all protected branches with "No one" as an access level will be
  changed to "Masters"

Magic Variable - Change the name of the variable to assign the local variable for partial, rather than `i` use the `index`.

Don't pass a local variable called `i` to a partial.

Fix skip_repo parameter being ignored when destroying a namespace

When destroying a namespace, the `skip_repo` parameter is supposed to prevent the repository directory from being destroyed and allow
the namespace after_destroy hook to run. If the namespace fails to be deleted for some reason, we could be left with repositories that are deleted with existing projects.

See merge request !5654

When destroying a namespace, the `skip_repo` parameter is supposed
to prevent the repository directory from being destroyed and allow
the namespace after_destroy hook to run. If the namespace fails
to be deleted for some reason, we could be left with repositories
that are deleted with existing projects.

change the API on the merge_request_diff model from diffs -> raw_diffs

## What does this MR do?

Unify diffs API

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## What are the relevant issue numbers?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- ~~[ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~
- ~~[ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~[ ] API support added~~
- Tests
  - ~~[ ] Added for this feature/bug~~
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5650

Speed up methods that depend on diff stats only

## What does this MR do?
Speeds up and reduces memory usage of `Commit#repo_changes`loop, `Repository#expire_avatar_cache` and `IrkerWorker`.  It's a WIP because it need a new version of `gitlab_git` released with [these changes](https://gitlab.com/gitlab-org/gitlab_git/merge_requests/109).

## Are there points in the code the reviewer needs to double check?
N/A

## Why was this MR needed?
For large files committed, this method ends up loading them in memory which can consume lots of memory.

## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/issues/19441#note_13425892

## Screenshots (if relevant)
N/A

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- ~~Tests~~
  - [ ] ~~Added for this feature/bug~~
  - [ ] ~~All builds are passing~~
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5568

Update the gitlab-shell version in the tmp/tests directory to the right version

Previously the gitlab-shell version would never be updated if the directory existed via the `gitlab:shell:install` Rake task. This could lead to incompatibility issues or random errors.

See merge request !5646