Originally branch 'mk-toggle-writing-to-auth-keys-1631'

See merge request !2004

Squashed commits:
Add authorized_keys_enabled to Application Settings
Ensure default settings are exposed in UI
Without this change, `authorized_keys_enabled` is unchecked when it is nil, even if it should be checked by default.
Add “Speed up SSH operations” documentation
Clarify the reasons for disabling writes
Add "How to go back" section
Tweak copy
Update Application Setting screenshot

Add find key by base64 key or fingerprint to the internal API

See merge request !250

Squashed changes:
Add unique index to fingerprint
Add new index to schema
Add internal api to get ssh key by fingerprint
Change API endpoint to authorized_keys
Add InsecureKeyFingerprint that calculates the fingerprint without shelling out
Add require for gitlab key fingerprint
Remove uniqueness of fingerprint index
Remove unique option from migration
Fix spec style in fingerprint test
Fix rubocop complain
Extract insecure key fingerprint to separate file
Change migration to support building index concurrently
Remove those hideous tabs

Fix custom name in branch creation for issue in Firefox

Closes #41563

See merge request gitlab-org/gitlab-ce!16244

API: get participants from merge_requests & issues

Closes #40986

See merge request gitlab-org/gitlab-ce!16187

Resolve "Create secrets failed for Auto DevOps with latest stable of kubectl"

Closes #41376

See merge request gitlab-org/gitlab-ce!16218

Backport 'Rebase' feature from EE to CE

Closes #40301

See merge request gitlab-org/gitlab-ce!16071

Remove the Project#repo method

See merge request gitlab-org/gitlab-ce!16238

Add docs about end-to-end testing / GitLab QA tests

Closes #39637

See merge request gitlab-org/gitlab-ce!16043

Expose project_id on /api/v4/pages/domains

See merge request gitlab-org/gitlab-ce!16200

Don't use Gitlab::Shell#import_repository on local paths

See merge request gitlab-org/gitlab-ce!16228

[EE-backport] Add group boards API endpoint

See merge request gitlab-org/gitlab-ce!16194

Backport of methods and components added in EE

See merge request gitlab-org/gitlab-ce!16208

Update redis-rack to 2.0.4

See merge request gitlab-org/gitlab-ce!16251

Update settings.md

See merge request gitlab-org/gitlab-ce!16233

Merge branch 'master' of gitlab.com:gitlab-org/gitlab-ce into 41563-fix-branch-creation-from-issue-in-firefox

Fix import project url not updating project name

Closes #40607

See merge request gitlab-org/gitlab-ce!16120

Add id to modal.vue to support data-toggle="modal"

Closes #41584

See merge request gitlab-org/gitlab-ce!16189

Up until version 2.0.3 redis-rack included a "rake" binary that would
overwrite/hijack the one provided by Rake itself. Unfortunately the
binary provided by redis-rack would produce errors in many cases. See
https://github.com/redis-store/redis-rack/pull/34 for more info.

Refactor cluster show page

Closes #41335

See merge request gitlab-org/gitlab-ce!16089

Allow local tests to use a modified Gitaly

Closes gitaly#833

See merge request gitlab-org/gitlab-ce!16220

Resolve "Verify integrity of repositories"

Closes #40228

See merge request gitlab-org/gitlab-ce!15931

Add online attribute to runner api entity

Closes #25774

See merge request gitlab-org/gitlab-ce!11750

Reroute batch blobs to single blob RPC

See merge request gitlab-org/gitlab-ce!16082

Prepare Gitlab::Git::Repository#rebase for Gitaly migration

See merge request gitlab-org/gitlab-ce!16192

Enclose props in double quotes for Item Stats in Groups tree app

See merge request gitlab-org/gitlab-ce!16231

Update some Gitaly annotations in Gitlab::Shell

See merge request gitlab-org/gitlab-ce!16226

Modify `LDAP::Person` to return username value based on attributes

Closes #39691

See merge request gitlab-org/gitlab-ce!15286

When a project uses fast-forward merging strategy user has
to rebase MRs to target branch before it can be merged.
Now user can do rebase in UI by clicking 'Rebase' button
instead of doing rebase locally.

This feature was already present in EE, this is only backport
of the feature to CE. Couple of changes:
* removed rebase license check
* renamed migration (changed timestamp)

Closes #40301

Resolve "Master failure due to static-analysis job in app/models/concerns/deployment_platform.rb"

Closes #41695

See merge request gitlab-org/gitlab-ce!16246