Enables frozen string for the following:

* lib/gitlab/hook_data/**/*.rb
* lib/gitlab/i18n/**/*.rb
* lib/gitlab/import/**/*.rb
* lib/gitlab/import_export/**/*.rb
* lib/gitlab/kubernetes/**/*.rb
* lib/gitlab/legacy_github_import/**/*.rb
* lib/gitlab/manifest_import/**/*.rb
* lib/gitlab/metrics/**/*.rb
* lib/gitlab/middleware/**/*.rb

Partially addresses gitlab-org/gitlab-ce#47424.

Hashed Storage: allow migration to be retried in partially migrated projects

Closes #53700

See merge request gitlab-org/gitlab-ce!23087

Provide application.css from master branch via GitLab Pages

Closes gitlab-ui#95

See merge request gitlab-org/gitlab-ce!23156

Remove unneeded licenses for gitlab-org npm namsepace

See merge request gitlab-org/gitlab-ce!23155

Docs agile sprints and releases

See merge request gitlab-org/gitlab-ce!22855

Check compilation of FE assets against multiple node versions

Closes #53813

See merge request gitlab-org/gitlab-ce!23068

Use @gitlab npm namespace

Closes gitlab-ui#65

See merge request gitlab-org/gitlab-ce!22629

minor: format fix for GH import page

See merge request gitlab-org/gitlab-ce!23152

Add information on support for git v2 in docs

See merge request gitlab-org/gitlab-ce!23138

Update architecture.md to have a component by component overview

See merge request gitlab-org/gitlab-ce!22472

Add missing `performance` to changelog type doc

See merge request gitlab-org/gitlab-ce!22733

Validate that foreign keys are indexed and created

Closes #50875

See merge request gitlab-org/gitlab-ce!22808

Resolve "Allow pipelines to be deleted by project owners"

Closes #41875

See merge request gitlab-org/gitlab-ce!22988

Rename diffs store variable

See merge request gitlab-org/gitlab-ce!23123

Replace weight icon

See merge request gitlab-org/gitlab-ce!23144

Refactor how a few ActiveRecord enums are defined

See merge request gitlab-org/gitlab-ce!23024

Fixed image discussion styling

Closes #54110

See merge request gitlab-org/gitlab-ce!23127

Object storage docs are not relevant to GitLab.com and is in Core

See merge request gitlab-org/gitlab-ce!22943

Fix punctuation error

See merge request gitlab-org/gitlab-ce!22345

Resolve "Upgrade Helm Tiller Version Used By GitLab Managed Apps"

Closes #49726

See merge request gitlab-org/gitlab-ce!22693

Merge branch '54011-all-files-named-index-have-their-content-rendered-as-if-they-were-text-files' into 'master'

Resolve "All files named `index.*` have their content rendered as if they were text files"

Closes #54011

See merge request gitlab-org/gitlab-ce!23063

Use Nokogiri as the ActiveSupport XML backend

Closes #54068

See merge request gitlab-org/gitlab-ce!23136

Add glob for CI changes detection

See merge request gitlab-org/gitlab-ce!23128

Fix typos in lib

See merge request gitlab-org/gitlab-ce!23106

Resolve "Can merge branch before build is started"

Closes #28682

See merge request gitlab-org/gitlab-ce!22911