Moving this method to a separate module looks a bit odd, but it allows
for EE to extend the method without also having to redefine a variety of
validation rules.

`Mentionable::ReferenceRegexes` used to define the following two
constants:

1. DEFAULT_PATTERN
2. EXTERNAL_PATTERN

These two constants were built using some of the class methods that
reside in this same module. In EE we redefine one of these methods by
using `prepend` at the start of the `ReferenceRegexes` module. This
poses a problem: we can not move the `prepend` to the end of the file,
because the constants later on depend on it.

To resolve this problem, this commit turns these constants into class
methods that memoize their results. This allows EE to redefine the
appropriate methods before these two class methods are used, in turn
allowing us to move the `prepend` to the end of the file.

See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8198 for more
information.

Dangerbot: mention tech writers based on DevOps stage

See merge request gitlab-org/gitlab-ce!22945

Bump Sidekiq and other related gems

See merge request gitlab-org/gitlab-ce!22956

Fix  ./spec/features/issues/user_views_issue_spec.rb

Closes gitlab-ee#8390

See merge request gitlab-org/gitlab-ce!22976

Add Discord integration

Closes #21635

See merge request gitlab-org/gitlab-ce!22684

Disable usage pings in review apps

See merge request gitlab-org/gitlab-ce!22965

Merge branch '53082-gitlab-ce-11-4-0-gemfile-conflict-gitlab-markup-and-github-markup' into 'master'

Update gitlab-markup gem to avoid binary name collision

Closes #53082

See merge request gitlab-org/gitlab-ce!22960

Fix some links and Markdown

See merge request gitlab-org/gitlab-ce!22972

CI randomly fails with:
    ActiveRecord::RecordNotFound:
       Couldn't find Project with 'id'=724

This is probably caused by DB cleanup strategy used for :js
tests in combination with `set`.

Update URLs to better ones

See merge request gitlab-org/gitlab-ce!22931

Fix link for raising helm chart issues

See merge request gitlab-org/gitlab-ce!22970

Add link in K8s integration docs to RBAC roles

See merge request gitlab-org/gitlab-ce!22941

Docs: Update Variable naming

See merge request gitlab-org/gitlab-ce!22352

See https://gitlab.com/gitlab-org/gitlab-ce/issues/53082

Fix error handling bugs in kubernetes integration

See merge request gitlab-org/gitlab-ce!22922

* Sidekiq changes:
  https://github.com/mperham/sidekiq/blob/master/Changes.md

* Rack 1.6.1 fixes CVE-2014-9490:
  https://github.com/rack/rack/blob/master/CHANGELOG.md

* rack-protection 2.0.4 only fixes a minor message:
  https://github.com/sinatra/sinatra/commits/master/rack-protection

Use gitlab-ui in jobs and pipelines

See merge request gitlab-org/gitlab-ce!22782

Remove circular dependency on Redactable in migration

See merge request gitlab-org/gitlab-ce!22951

Resolve "GitLab Pages settings regressions"

Closes #48475

See merge request gitlab-org/gitlab-ce!22821

Updates clipboard button with gitlab-ui

See merge request gitlab-org/gitlab-ce!22923

Gitlab::BackgroundMigration::RedactLinks was prepending
EE::Gitlab::BackgroundMigration::RedactLinks, while
EE::Gitlab::BackgroundMigration::RedactLinks was trying to include
Gitlab::BackgroundMigration::RedactLinks::Redactable. Ruby 2.5.3 failed
with an uninitialized constant
(https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/118388511).

Fix alignment of diff comment buttons

Closes #53768

See merge request gitlab-org/gitlab-ce!22944

Fix DashboardHelper reference in spec

See merge request gitlab-org/gitlab-ce!22948

Helpers::DashboardHelper doesn't actually exist, and Ruby 2.5 gets rid
of the automatic top-level constant lookup
(https://bugs.ruby-lang.org/issues/11547).

Resolve possible cherry pick API race condition

Closes #53773

See merge request gitlab-org/gitlab-ce!22946

Enable even more frozen string in lib/gitlab

See merge request gitlab-org/gitlab-ce!22863

Symlinked hooks aren't executed

See merge request gitlab-org/gitlab-ce!22933

Ensure we create the secrets at the right time

Closes #53621

See merge request gitlab-org/gitlab-ce!22938