SSoT for customization docs

Closes #64588

See merge request gitlab-org/gitlab-ce!31308

Reviewed all docs in the customization section
and updated them to adhere to our SSoT standards.

Update reliable fetcher

See merge request gitlab-org/gitlab-ce!31416

Add note about refactoring to board_service.js

See merge request gitlab-org/gitlab-ce!31468

Docs: add addon minute roll over info

See merge request gitlab-org/gitlab-ce!31350

Merge branch '65386-docs-add-elasticsearch-troubleshooting-to-administrator-troubleshooting-section' into 'master'

Docs-Add ElasticSearch Troubleshooting

Closes #65386

See merge request gitlab-org/gitlab-ce!31343

* Added elasticsearch.md
* Added reference to guide in Troubleshooting section

Use Rails 5.2 Redis caching store

Closes #64794

See merge request gitlab-org/gitlab-ce!30966

Fix links to unassigned, low weight issues for first time contributors

See merge request gitlab-org/gitlab-ce!31485

(Really) Fix Ruby 2.5 compatibility for diverging counts of branches

Closes #64143

See merge request gitlab-org/gitlab-ce!31491

We added retry_count increment when job is recovered

Fix Admin area user access level radio button labels

See merge request gitlab-org/gitlab-ce!31154

In the admin user edit form, access level radio button labels didn't have
the correct 'for' value. Clicking on the label did not select the radio
button. This makes usability a bit nicer since the click area is increased
when the label is clickable.

This is the first step in providing a fault-tolerant and distributed
Redis caching store. We disable compression to avoid introducing a
change that could have an adverse effect in production.

Note that we won't be able to take advantage of the fault-tolerance and
distributed features yet until we solve
https://gitlab.com/gitlab-org/gitlab-ce/issues/64829.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/64794

!31480 does not fully restore compatibility because another Ruby 2.6
feature besides `Enumerable#filter` was used in commit ca5cd7b7. The use
of `Enumerable#to_h`'s block is now replaced by an explicit
`Enumerable#map` call.

Error message:

	TypeError (wrong element type Gitlab::Git::Branch at 0 (expected array)):
  	app/controllers/projects/branches_controller.rb:53:in `to_h'

See https://bugs.ruby-lang.org/issues/15143.

Fixes #64143.

Resolve "Add padding to "merged by" widget"

Closes #64831

See merge request gitlab-org/gitlab-ce!30972

This reverts commit c3751046d217008404a0bd371e59d6ffd6734923.

Update dependency @gitlab/ui to v5.14.0

See merge request gitlab-org/gitlab-ce!31482

Add example to plugins file

See merge request gitlab-org/gitlab-ce!30508

Add description how to set custom CI file

See merge request gitlab-org/gitlab-ce!31445

Fix error on project name

See merge request gitlab-org/gitlab-ce!31471

Add project path to sql query to build proper path

[ci skip]

Resolve "API endpoint to list the Docker images/tags of a group"

See merge request gitlab-org/gitlab-ce!30817

API endpoints for requesting container repositories
and container repositories with their tag information
are enabled for users that want to specify the group
containing the repository rather than the specific project.

Only track Redis calls if Peek is enabled

See merge request gitlab-org/gitlab-ce!31438

Removed external dashboard legend border

Closes #64675

See merge request gitlab-org/gitlab-ce!31407

Fixed bug from extra parenthesis

Closes #63474

See merge request gitlab-org/gitlab-ce!31479

Bring diagnostics_tools.md from debug project to docs

See merge request gitlab-org/gitlab-ce!31399

Document when quotes aren't needed for quick actions

Closes #63735

See merge request gitlab-org/gitlab-ce!31338

Add missing timezone when copying legacy artifacts (ci_builds)

See merge request gitlab-org/gitlab-ce!31447