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.

So they are reusable for EE later

When there were `AccessLevels` for users/groups in the protected
branch. The CE view doesn't handle those correctly.

So a specific view for EE has been added to deal with the case.

It also shows the users/groups that still have access.

In this case `app/models/concerns/protected_ref_access` had EE
specific code in `app/models/ee/protected_ref_access`. It should have
been `app/models/concerns/ee/protected_ref_access`.

That way they are available to the dispatcher and don't need to be
imported there.

And bring the views from CE into EE as a fallback when the feature
isn't available

And move the EE files into `EE` folder.

When the feature isn't available

And move the EE-specifics into a separate bundle

And restore the CE views to be able to fall back to them when the
feature is not available