Enables frozen string for the following:

* app/controllers/*.rb
* app/controllers/admin/**/*.rb
* app/controllers/boards/**/*.rb
* app/controllers/ci/**/*.rb
* app/controllers/concerns/**/*.rb

Partially addresses #47424.

Remove EE-specific lines from Plan concerns

See merge request gitlab-org/gitlab-ce!21448

Enhance some performance guideline titles

See merge request gitlab-org/gitlab-ce!21797

[QA] consolidate selector patterns (1_manage/login)

See merge request gitlab-org/gitlab-ce!21711

Improve Emoji detection in commit messages

Closes gitlab-org/release/framework#15

See merge request gitlab-org/gitlab-ce!21799

Resolve "Enable Auto DevOps by default for self managed instances of GitLab"

Closes #41729

See merge request gitlab-org/gitlab-ce!21157

Improve cluster apps installation flow

Closes #50111

See merge request gitlab-org/gitlab-ce!21567

Improve TabHelper to clarify the use of Namespaces for the nav_link

See merge request gitlab-org/gitlab-ce!21787

Don't use MilestoneFinder for group milestones

Closes #51546

See merge request gitlab-org/gitlab-ce!21780

Document the use of and need for using feature flags more frequently

See merge request gitlab-org/gitlab-ce!21478

This adds a development guide explaining that we are going to use
feature flags more often, why, what the benefits are, and so on.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/49619 for more
information.

Resolve "Move filter dropdown from Font Awesome to our own icons"

Closes #46733

See merge request gitlab-org/gitlab-ce!21694

This refactors the DashboardGroupMilestone model so that it no
longer uses the MilestoneFinder, instead using methods defined
on the Milestone model directly.

This changes our Danger integration so that it is smarter about
detecting GitLab emoji in commit messages. This is done using a two step
process:

1. We use the old regular expression to determine if a commit message
   _might_ include an emoji.

2. If this regular expression matches, we then check for all existing
   emoji names in the commit message. This might be a wee bit expensive,
   but because we couple it with the previous step it should be rarely
   executed.

This ensures we don't trigger an error when a commit message includes
text such as `:foo:bar:`, which is not a valid Emoji.

Fixes https://gitlab.com/gitlab-org/release/framework/issues/15

This enhances a few performance guideline titles in the development
README, making it easier to understand what topics they cover.

Respect the user commit email in more places

Closes #51564

See merge request gitlab-org/gitlab-ce!21773

Update database requirements documentation with more MySQL limitations

See merge request gitlab-org/gitlab-ce!21686

Correct usage of the have_link matcher

See merge request gitlab-org/gitlab-ce!21755

Resolve "Open issues from archived project listed in group issue board"

Closes #45754

See merge request gitlab-org/gitlab-ce!21721

Resolve character encodings in CONTRIBUTING

See merge request gitlab-org/gitlab-ce!21781

Expose runners status information in job api

Closes #51273

See merge request gitlab-org/gitlab-ce!21618

Return a default commit email if migration has not completed

Closes #51530

See merge request gitlab-org/gitlab-ce!21790

QA: Fix: set initial password even if using admin credentials

See merge request gitlab-org/gitlab-ce!21785

Add a new scenario to add an SSH key, perform Git actions with it, and then remove the key

See merge request gitlab-org/gitlab-ce!19754

Fix haml-lint error in 2FA codes partial

Closes #51585

See merge request gitlab-org/gitlab-ce!21786

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51585

Allow UrlValidator to work with attr_encrypted

See merge request gitlab-org/gitlab-ce!21776

Sync commonmaker version in Gemfile.*.lock

Closes #51557

See merge request gitlab-org/gitlab-ce!21782