Add docs on multi-project pipelines mini graph

Closes #2938

See merge request !2450

Refactor GitLab Slack app docs

Closes #2862

See merge request !2447

Update health check docs

See merge request !2446

Add small fixes in Canary deployments docs

See merge request !2449

Update links to groups doc

See merge request !2442

Llink new doc (Related Issues) from indexes pages

See merge request !2443

Add subgroups limitations to Pages docs

Closes gitlab-ce#34621

See merge request !2444

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/2862

Update MR index doc

See merge request !2433

Fix history button padding

Closes gitlab-ce#35090

See merge request !2438

Refactor + overview and use cases for Groups-related EE-only features

See merge request !2385

Add use cases for squash and fast forward MR docs

Closes #2814

See merge request !2384

Namespace license checks Audit Events & Admin Audit Log

Closes #2583

See merge request !2326

Fix undefined method quote when database load balancing is used

Closes gitlab-ce#35097

See merge request !2430

Fix implicit license plans

Closes #2929

See merge request !2427

CE upstream: Thursday

Closes gitlab-shell#92, gitaly#356, gitlab-ce#34853, and gitlab-ce#34941

See merge request !2422

Licenses without a plan specified need to act as though they are EES. This is
currently implemented for licenses that don't include a plan in their data at
all, but if `plan: nil` or `plan: ""` is set, the customer loses access to a
number of features with license checks added in 9.4. This commit changes the
license check to use the starter plan in those cases too.

Add a license check for permissions to users/groups on protected refs

Closes #2574

See merge request !2320

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/35097

Document Code Quality limitation

See merge request !2428

Merge request approvals before merge should be nil if unavailable

Closes gitlab-ce#35082

See merge request !2426

AuditEventService has some EE-only methods, so move them to a separate
file.

For logging events, user events are always allowed, since they are in
CE too.

When Admin Audit Log is enabled, there is also some more details logged.