Grapify boards API

## What does this MR do?

Add the Grape-DSL to the boards API.

## What are the relevant issue numbers?

Related to #22928

See merge request !6876

Updated issuable dropdown titles

## What does this MR do?

The dropdowns in the issuable form still had the filter dropdown titles, this fixes that by giving them their own titles.

Closes #23337

See merge request !6882

Fix grafana_configuration.md move link

See merge request !6871

Show deployed time ago

Closes #21652

cc @ayufan 

See merge request !6676

Reassign secret token when regenerating one

## What does this MR do?

This is an attempt to fix intermittent errors in out test suite.

```text
Failures:

  1) Gitlab::Shell memoized secret_token creates and links the secret token file
     Failure/Error: expect(File.read(secret_file).chomp).to eq(secret_token)
     
       expected: "690f959e206ab91acc54e1c605c7ff90"
            got: "cccb4e8df9360600271e61114d4e6e68"
     
       (compared using ==)
     # ./spec/lib/gitlab/backend/shell_spec.rb:47:in `block (3 levels) in <top (required)>'
```

It appears that `spec/lib/gitlab/backend/shell_spec.rb` tries to change the file that stores secret token, but `Gitlab::Shell` memoizes `@secret_token` on class level, so when it was already created by other tests (`spec/requests/api/internal_spec.rb` in this case), memoized token is not reassigned even if it was generated again with `ensure_secret_token!`.

See merge request !6844

Grapify todos API

## What does this MR do?

Add the Grape-DSL to the todos API.

## What are the relevant issue numbers?

Related to #22928

See merge request !6875

Extract project#update_merge_requests to its own worker from GitPushService

See merge request !6767

Closes #23337

Resolve "Fix missing Glossary link"

## What does this MR do?

Fixes broken links in University.

## What are the relevant issue numbers?

Closes #23332

See merge request !6880

Grapify system hooks API

## What does this MR do?

Add the Grape-DSL to the system-hook API.

## What are the relevant issue numbers?

Related to #22928

See merge request !6861

Add more info on the new CI permissions model

From discussion in issue https://gitlab.com/gitlab-org/gitlab-ce/issues/22484

See merge request !6843

Refactor merge requests revisions docs

See merge request !6878

- A system note now appears on every push
- Replace dashes with underscores in images

[ci skip]

Link to review apps example from docs

Put a link in the example project of the Review Apps in dynamic environments
and to the list of CI examples.

See merge request !6873

[ci skip]

Do not run before_script, artifacts, cache in trigger_docs job

Fixes

See merge request !6866

Replace unique keyframes mixin with specific keyframe animation names

## What does this MR do?
Replaces `unique-keyframes` mixin with `include-keyframes` mixin

## Are there points in the code the reviewer needs to double check?
Shouldn't be 👍🏻 

## Why was this MR needed?
Some users had GitLab hosted in a distributed environment that makes `unique-keyframes` a non-viable implementation. 
The randomized animation names from `unique-keyframes` was not being picked up by the different servers which resulted in 404 errors.

## 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
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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)

## What are the relevant issue numbers?
Closes #22629

See merge request !6603

CE to EE merge check rake task

## What does this MR do?

This merge request adds a Rake task that checks whether the current branch can be merged cleanly to EE/master.

If not, it checks if a `<ce_branch>-ee` branch exists in EE, tries to merge it to EE/master and then tries to merge `ce_branch` to EE/master.

If the result of the check is that the current branch cannot be merged cleanly to EE/master, the job will fail, display troubleshooting steps, and a warning will be shown in the merge request.

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

Probably the steps I used to do the various checks, and also the steps I suggest to create an EE-specific branch.

## Why was this MR needed?

The goal is to catch as early as possible the possible conflicts a CE MR will cause when CE/master will be merged to EE/master. This way, the developer is warned that he/she should open a MR against EE before or as soon as the CE is merged. In the end, this should lower the work of the CE->EE merger.

## What are the relevant issue numbers?

Part of gitlab-org/gitlab-ee#715, hopefully.

See merge request !6746

Handle case where deployment ref no longer exists

## What does this MR do?

In 8.9, we didn't create keep-around refs for deployments. So it's possible that someone created a deployment (say, for testing), and then deleted the branch and all other references to that commit. That commit could then get GCed, and trying to view MRs on 8.11+ will show a 500. See https://gitlab.com/gitlab-org/gitlab-ce/issues/22655#note_16575020 for more details.

## Why was this MR needed?

If someone created a deployment on 8.9, then deleted all references to the commit for that deployment, we will throw an exception when checking if the deployment includes a commit.

Closes #22655.

See merge request !6855

Sort API mounts

## What does this MR do?

Sort the API mounts.

## Why was this MR needed?

The API mounts are unsorted.

See merge request !6831

Convert unicode emojis to images.

## Why was this MR needed?

For better cross platform interoperability with emojis.

Closes #22591

See merge request !6829

Also add a safeguard for non-CI env.
Signed-off-by: Rémy Coutable <remy@rymai.me>