Add notices about disabling auth features for users with 2FA.

Related to #2979

- Document the proposed changes to the GitLab authentication system.
- This is done because currently, users with 2FA enabled are allowed API access without a 2FA token.

# Tasks

- [ ]  #2979 !xxxx - Document proposed auth changes for 2FA users
    - [x]  Wait for replies on "[potential avenues for documenting the planned changes](https://gitlab.com/gitlab-org/gitlab-ce/issues/2979#note_12591578)"
    - [x]  Update documentation
    - [ ]  CHANGELOG entry?
    - [ ]  Merge conflicts

See merge request !4815

Improve validations and error handling in new CI config entries

## What does this MR do?

This MR improves validation in new CI config.

## Why was this MR needed?

With that it will be easier to handle errors during validation and post-processing.

## What are the relevant issue numbers?

This is a continuation of #15060

See merge request !4560

Clean up some unused templates imported from GitLab CI

## What does this MR do?

Clean up some unused templates imported from GitLab CI, for new developers to easily understand the file/directory structure of Gitlab CE.

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

Be sure if removed files are not used now while the committer checked them once.

## Why was this MR needed?

Because the file/directory structure of the repository should be clear and simple and if so new developers can easily understand the file/directory structure of Gitlab CE.

## What are the relevant issue numbers?

Closes #19158 

## Does this MR meet the acceptance criteria?

- CHANGELOG won't be updated due to repository maintenance
- No documentation created/updated
- No API support added
- Tests
  - [skipped] 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 !4922

Add debugging tips with gdb



See merge request !4522

Removed unneeded word

Pretty simple, improved the wording a bit.

See merge request !4920

[ci skip]

Validate presence of essential params for diff rendering

## What does this MR do?

Check the presence of essential params before rendering diff content.
## Are there points in the code the reviewer needs to double check?

No
## Why was this MR needed?

To avoid the generated application error
## What are the relevant issue numbers?

#19096

## 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
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [ ] 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)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4917

This will avoid application errors generated by the assumption of the
presence of these params.

Fix issue being ordered twice and callback when moving between states

fixes #15588 

See merge request !4296

Upgrade sentry-raven from 0.15.6 to 1.1.0.

Changelog: https://github.com/getsentry/raven-ruby/releases

Closes #18804

See merge request !4913

Re-implement page-specific JS in a better way.

## What does this MR do?

This rebuilds the way we do page-specific JavaScript assets for a few reasons:

- The current implementation does not work with Subresource Integrity (!4808)
- The current implementation doesn't allow caching of libraries because each page we hook up with this system will have a separate application.js. Meaning that for every page that uses Ace Editor, we'd have to load Ace Editor plus any GitLab-specific scripts in the same file, making local caching of just Ace Editor impossible.
- The current implementation is rather hacky.

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

That Sprockets doesn't choke on this when we use precompiled assets.

## What are the relevant issue numbers?

#14372

## 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)

cc: @jschatz1 @pavelloz

Thanks to @pavelloz for his example implementation which was very useful.

See merge request !4883

Add SMTP as default delivery method to match gitlab-org/omnibus-gitlab!826

Something happened after upgrading to 8.9RC5 that caused mail settings to be set to sendmail by default. gitlab-com/infrastructure#128 describes the issue in more detail. This MR mirrors the change in omnibus with gitlab-org/omnibus-gitlab!826.

Closes #19132

See merge request !4915

Closes #19132

[ci skip]

Fix a wrong MR status when merge_when_build_succeeds & project.only_allow_merge_if_build_succeeds are true

## What does this MR do?

Fix a wrong MR status when merge_when_build_succeeds & project.only_allow_merge_if_build_succeeds are true.

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

@stanhu I reused your proposal from the issue, I think it's a good enough solution.

## What are the relevant issue numbers?

Fixes #19035.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] 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)
- [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 !4912

Changelog: https://github.com/getsentry/raven-ruby/releases

Fix a wrong MR status when merge_when_build_succeeds & project.only_allow_merge_if_build_succeeds are true

The issue was that `MergeRequest#mergeable?` returns false when the CI
state is not success and project.only_allow_merge_if_build_succeeds is
true. In this case `Projects::MergeRequestsController#merge` would
return the `:failed` status when enabling `merge_when_build_succeeds`,
thus leading to a weird state and the MR never automatically merged.

The fix is to disable the CI state check in the controller safeguard
that early return the `:failed` status.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Disable the email checking part of the standard Health Check

## What does this MR do?
    
In order to fix it we have overwritten the email_configured? method in the health check so that it does not check email status during the standard health check.

## Why was this MR needed?

The email check used in the Heath Check doesn't properly make use of enough of the SMTP config options to be able to properly test the STMP connection, and as a result could cause a failure.

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17742

## 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
  - [ ] 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 !4903

Fixed award emoji changelog entry

See merge request !4910

This is meant to go in 8.9.1, not 8.10.0.

[ci skip]

[ci skip]

There was nothing additional in the full checks that we want to run (email, custom)

Update default regexp documentation to match reality

The regexp was updated in 8172d2c1 but this was stale.


See merge request !4866

The email check used in the Heath Check doesn't properly make use of enough of the SMTP config options
to be able to properly test the STMP connection, and as a result could cause a failure.

In order to fix it we have overwritten the email_configured? method in the health check
so that it does not check email status during the standard health check.

Added changelog entry for redacting improvements

See merge request !4896

[ci skip]

Fix temp file being deleted after the request while importing a GitLab project

Fixes https://gitlab.com/gitlab-com/infrastructure/issues/151

In production, the temporary uploaded file is getting deleted straight after the request so the Sidekiq worker is unable to find it in `/tmp`

Also, improved erroring/logging of this situation.

See merge request !4894

Support for rendering/redacting multiple documents

See merge request !4828

This commit changes the way certain documents are rendered (currently
only Notes) and how documents are redacted. Previously both rendering
and redacting would run on a per document basis. The result of this was
that for every document we'd have to run countless queries just to
figure out if we could display a set of links or not.

This commit changes things around so that redacting Markdown documents
is no longer tied into the html-pipeline Gem. This in turn allows it to
redact multiple documents in a single pass, thus reducing the number of
queries needed.

In turn rendering issue/merge request notes has been adjusted to take
advantage of this new setup. Instead of rendering Markdown somewhere
deep down in a view the Markdown is rendered and redacted in the
controller (taking the current user and all that into account). This has
been done in such a way that the "markdown()" helper method can still be
used on its own.

This particular commit also paves the way for caching rendered HTML on
object level. Right now there's an accessor method Note#note_html which
is used for setting/getting the rendered HTML. Once we cache HTML on row
level we can simply change this field to be a column and call a "save"
whenever needed and we're pretty much done.

Fix tmp file being deleted after the request plus some cleanup and improved erroring for this situation

Fix settings_spec so that it can that run by itself

Running `spec/settings_spec.rb` would fail because it would attempt to load `1_settings.rb`, which would reference `Rails`. This constant was not loaded without `spec_helper.rb`.


See merge request !4893

Replace Haml with Hamlit

What this change does:
- It replaces HAML with [Hamlit](https://github.com/k0kubun/hamlit), a much more efficient implementation of HAML.
- It removes `haml-rails`.
- It adds `hamlit.rb` and removes `haml.rb`.
- It makes things faster and less memory-hungry!

See also #13201.

See merge request !3666