Extend documentation on writing EE features

See merge request !2248

Used to guard EE-licensed features.

CE upstream: Friday

Closes gitaly#464, gitlab-com/community-writers#40, gitlab-ce#36618, gitaly#468, #3149, gitlab-ce#36492, and gitlab-ce#3646

See merge request !2710

* ee/master:
  Geo - Remove unnecessary param from Geo::BaseSyncService#update_registry
  [ci skip] Geo: add documentation on what selective replication support
  Update multi_project_pipeline_graphs.md
  Drop unnecessary timestamp columns in Geo event tables

[ci skip] Geo: add documentation on what selective replication support

Closes #3161

See merge request !2734

Geo - Remove unnecessary param from Geo::BaseSyncService#update_registry

See merge request !2735

Drop unnecessary timestamp columns in Geo event tables

See merge request !2714

Update multi_project_pipeline_graphs.md

Closes #2938

See merge request !2727

* ee/master:
  Hide admin Audit Log in sidebar when not licensed

Hide admin Audit Log in sidebar when not licensed

Closes #3197

See merge request !2726

See: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2710
and: https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/29653003

* ee/master:
  Removes Gitlab::Metrics usage from StuckImportJobsWorker
  Fixes Audit Events Documentation issue link
  Add more sections in GPG docs
  Refactor GPG signing docs
  Change GPG docs location
  Fix store credentials
  Refactor `push_rule_check` GitAccess specs
  Fix invalid GitAccess specs for License and secondary Geo node
  Make issuable filter dropdown style consistent
  Refactor `run_group_permission_checks` helper in GitAccess spec
  Reduce duplication in GitAccess spec around error messages
  Greatly reduce test duration for git_access_spec
  Hijack AR::Base.connection in the DB load balancer
  Added time fields for csv export
  Use gitlab.yml.example instead of settings logic stubbing
  Fix url for object store artifacts
  fix Modify commit message button spacing

Removes Gitlab::Metrics usage from StuckImportJobsWorker

See merge request !2728

Hijack ActiveRecord::Base.connection in the DB load balancer

Closes #3191

See merge request !2707

See gitlab-org/gitlab-ee!2483

Also for permitted params use a prepended EE module to define the list
of accepted attributes (calling `super`).

One more example how EE-feature regressions can be avoided.

Add some more context about how EE should act as CE when no valid
license is provided.

Only show the Audit Log in the Admin sidebar when the installation has
a valid EE license to use that feature.

[EE] Greatly reduce test duration for git_access_spec

See merge request !2719

fix Modify commit message button spacing

Closes #3163

See merge request !2693

Fixes Audit Events Documentation issue link

See merge request !2725

Refactor GPG docs

See merge request !2724

Fix url for object store artifacts

Closes #3172

See merge request !2705

1. Generating a GPG key
1. Signing commits
1. Associating a GPG key with Git