Fix header links in PG and Redis HA/Scaling docs

See merge request gitlab-org/gitlab-ee!9668

Docs: add details about restricted SSH keys

Closes #50489

See merge request gitlab-org/gitlab-ce!25478

Add an index page to admin area section

Closes #55234

See merge request gitlab-org/gitlab-ce!25375

Add an index page to admin area section

See merge request gitlab-org/gitlab-ee!9601

Changes to HA docs to inc different architecture types

See merge request gitlab-org/gitlab-ee!9174

Resolve "/admin/runners page fails with an SQL Statement Timeout"

Closes #53325

See merge request gitlab-org/gitlab-ce!25220

Lower the allowed Gitaly call count to 30

See merge request gitlab-org/gitlab-ce!25467

Prior to this change, 35 Gitaly RPCs were allowed. But recently there's
been a renewed interest in performance. By lowering the number of
calls new N + 1's will pop up.

Later commits will add blocks to ignore the raised errors, followed by
an issue for each to be fixed.

Split Severity and Confidence values for vulnerability occurrences

Closes #9397

See merge request gitlab-org/gitlab-ee!9495

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/9397

Ensure all lists are surrounded by new lines

See merge request gitlab-org/gitlab-ce!25479

Markdown renderers find it easier to determine
where lists start and end when lists are surrounded
by new lines.

For consistency, also ensure entries in the list
are aligned when they span multipls lines.

Port from CE: Ensure all lists are surrounded by new lines

See merge request gitlab-org/gitlab-ee!9659

Markdown renderers find it easier to determine
where lists start and end when lists are surrounded
by new lines.

For consistency, also ensure entries in the list
are aligned when they span multipls lines.

Improve snippets empty state

Closes #44045 and #20847

See merge request gitlab-org/gitlab-ce!18348

EE: Improve snippets empty state

See merge request gitlab-org/gitlab-ee!9650

Only show borders around markdown images in notes

Closes #55703

See merge request gitlab-org/gitlab-ce!25448

Resolve "Fix danger commit messages check"

Closes #58057

See merge request gitlab-org/gitlab-ce!25489

Quarantine code owners test

See merge request gitlab-org/gitlab-ee!9662

Skip user auth check in alerts_controller#notify

Closes #9504

See merge request gitlab-org/gitlab-ee!9636

Do not check if the user can read project in the notify action of the
alerts_controller because that API is hit by alertmanager, and there
will never be a user signed in. Project access will be checked in
the NotifyService which checks if the alertmanager token in the request
matches the token in the DB for the given project.

Update dependency @gitlab/svgs to ^1.54.0

See merge request gitlab-org/gitlab-ce!25488

Port EE System Header And Footer feature to CE

Closes #55057

See merge request gitlab-org/gitlab-ce!25241

Port of 55057-system-message-to-core to EE

See merge request gitlab-org/gitlab-ee!9556