Update ES indexer docs for Omnibus users

Closes #63207

See merge request gitlab-org/gitlab-ce!29731

Fix linebreak rendering in Mermaid flowcharts

Closes #54588

See merge request gitlab-org/gitlab-ce!30730

Clean-up some confusing info from security docs

See merge request gitlab-org/gitlab-ce!29495

Avoid using HTML when plain text and markdown work

See merge request gitlab-org/gitlab-ce!30768

Add nfs autodetection section in NFS docs

Closes gitaly#1767

See merge request gitlab-org/gitlab-ce!30486

Fix links to documentation styleguide

See merge request gitlab-org/gitlab-ce!30732

Using the old link redirects to
https://docs.gitlab.com/ee/development/documentation/index.html
which does not show the mentioned documentation.

Add usage of `default:`

Closes #63351

See merge request gitlab-org/gitlab-ce!30677

Update job artifact download docs

See merge request gitlab-org/gitlab-ce!30714

Create docs for required pipeline config

See merge request gitlab-org/gitlab-ce!30660

Check for "Uninstall" button reducing friction

See merge request gitlab-org/gitlab-ce!30713

Clean up the Prometheus custom dashboards docs

See merge request gitlab-org/gitlab-ce!30582

- Place all under one section
- Fix Markdown

Merge branch 'docs/12733-docs-using-multiple-extends-in-gitlab-ci-yml-introduced-in-gitlab-12' into 'master'

Specify what version of multiple extends in docs

Closes gitlab-ee#12733

See merge request gitlab-org/gitlab-ce!30667

SSoT for administration/high_availability docs

Closes #64560

See merge request gitlab-org/gitlab-ce!30729

- Make sure we have type defined in the frontmatter
- Add troubleshooting sections where absent
- Meaningful intros where absent

SSoT for administration/auth docs

Closes #64559

See merge request gitlab-org/gitlab-ce!30727

- Make sure we have type defined in the frontmatter
- Add troubleshooting sections where absent
- Meaningful intros where absent

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/39964

Closes #39964

See merge request gitlab-org/gitlab-ce!30722

Fix broken vue i18n strings

See merge request gitlab-org/gitlab-ce!30753

Docs: Add more detail to sign-up restrictions

See merge request gitlab-org/gitlab-ce!30580

Document openstack object store configuration

See merge request gitlab-org/gitlab-ce!30659

Liek asked in gitlab-org/gitlab-ce#59501

Update markdown.md to remove typo, "test" was left in the documentation

See merge request gitlab-org/gitlab-ce!30752

Align container registry empty state with design guidelines

Closes #64249

See merge request gitlab-org/gitlab-ce!30502

Shortened descriptive text
Added copy button to code snippets

Move setCurrentBoard() from BoardsStoreEE to core  (CE-backport)

See merge request gitlab-org/gitlab-ce!30626

(cherry picked from commit 9cd745c65bcb51d615399e82d8b26ef5cce972e1)

Unquarantine Add Deploy Key test

See merge request gitlab-org/gitlab-ce!30756

Add an appropriate solution in QA E2E style guide example

See merge request gitlab-org/gitlab-ce!30761

A "bad" example was given, however no solution was provided
for fixing the bad example