Resolve "DOCS Clarify usage of ElasticSearch with Gitaly non-NFS"

Closes #65606

See merge request gitlab-org/gitlab-ce!31454

Edit new troubleshooting doc

See merge request gitlab-org/gitlab-ce!31512

Cross link between cluster topics

Closes #65617

See merge request gitlab-org/gitlab-ce!31506

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.

Remove titles from security-links in sidebars

See merge request gitlab-org/gitlab-ee!14949

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

Add note about refactoring to EE-specific board_service.js

See merge request gitlab-org/gitlab-ee!14993

MVC: Group and User Billing Page Improvement - Avatar and Name

Closes #12843 and #12797

See merge request gitlab-org/gitlab-ee!14660

Fix min approvals required for new MR rules

See merge request gitlab-org/gitlab-ee!14988

Both top-level navigation items that link to the projects'
and the group's security dashboard contain title-attributes.

This is inconsistent with the rest of the navigation.

This commit removes the title-attributes for both elements.

Docs: add addon minute roll over info

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

Remove some old feature flags from devops::secure

See merge request gitlab-org/gitlab-ee!14983

The corresponding features are running since several releases

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

Allow approvals_required to be lower than project

See merge request gitlab-org/gitlab-ee!14902

MR level approvals_required are currently restricted to be higher
than project level approvals_required.

This removes that restriction so the logic will be simpler.

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

EE: Fix Admin area user access level radio button labels

See merge request gitlab-org/gitlab-ee!14844

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.