Port of https://dev.gitlab.org/gitlab/gitlab-ee/merge_requests/866
to CE excluding the migration and service changes as they don't
apply to CE.

[ci skip]

Add missing provider_unauthorized method to import_github.rb

Closes #60347

See merge request gitlab-org/gitlab-ce!27218

Update GitLab Workhorse to v8.6.0

See merge request gitlab-org/gitlab-ce!27260

Increase clusters bundle specs timeout

Closes #60398

See merge request gitlab-org/gitlab-ce!27269

Resolve "Long file names in MR diffs cause horizontal scrolling"

Closes #60304

See merge request gitlab-org/gitlab-ce!27233

Revert "Remove HipChat integration from GitLab"

Closes #60042

See merge request gitlab-org/gitlab-ce!27172

Quarantine Issue suggestions spec

See merge request gitlab-org/gitlab-ce!27259

Better documentation on repo mirroring enqueuing

Closes gitlab-ee#10345

See merge request gitlab-org/gitlab-ce!27093

Docs: Refactor Pages' intro guide

See merge request gitlab-org/gitlab-ce!27136

Remove redundancies:
- Domains
- User/group/project sites

Edits for GKE whitepaper note

Closes gitlab-ee#11103

See merge request gitlab-org/gitlab-ce!27243

Fixes Web IDE not loading merge request files

Closes #60243

See merge request gitlab-org/gitlab-ce!27225

Revert "Merge branch '24704-download-repository-path' into 'master'"

See merge request gitlab-org/gitlab-ce!27249

Fix ApplicationSetting development seed

Closes #60278

See merge request gitlab-org/gitlab-ce!27213

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/60243

Merge branch '59928-fix-the-following-style-lint-errors-and-warnings-for-app-assets-stylesheets-pages-stat_graph-scss' into 'master'

Resolve "Fix the following style-lint errors and warnings for `app/assets/stylesheets/pages/stat_graph.scss`"

Closes #59928

See merge request gitlab-org/gitlab-ce!27180

Process at most 4 pipelines during push

See merge request gitlab-org/gitlab-ce!27205

Merge branch 'ce-6120-extract-ee-specific-files-lines-for-spec-services-merge_requests' into 'master'

[CE-port] Extract EE specific files/lines for spec/services/merge_requests

See merge request gitlab-org/gitlab-ce!26977

This reverts commit 6c75bd01, reversing
changes made to 1be7f5aa.

Guard against nil dereferenced_target

Closes #60076

See merge request gitlab-org/gitlab-ce!27192

Enable eslint-plugin-jest for Jest

Closes #59636

See merge request gitlab-org/gitlab-ce!26715

Delete static_fixtures.rb for static HAML fixtures

Closes #59200

See merge request gitlab-org/gitlab-ce!27145

Fix styling for `app/assets/stylesheets/pages/detail_page.scss`

Closes #59909

See merge request gitlab-org/gitlab-ce!26873

Add @ashmckenzie to backend CODEOWNERS

Closes gitlab-com/www-gitlab-com#3353

See merge request gitlab-org/gitlab-ce!27204

Merge branch '10017-move-ee-differences-for-app-assets-javascripts-boards-models-list-js' into 'master'

Backport of Resolve "Move EE differences for `app/assets/javascripts/boards/models/list.js`"

See merge request gitlab-org/gitlab-ce!27198

Merge branch '10016-move-ee-differences-for-app-assets-javascripts-boards-models-issue-js' into 'master'

Backport of "Move EE differences for `app/assets/javascripts/boards/models/issue.js`"

See merge request gitlab-org/gitlab-ce!27197

Align UrlValidator to validate_url gem implementation

See merge request gitlab-org/gitlab-ce!27194

Renamed UrlValidator to AddressableUrlValidator to avoid 'url:' naming collision with ActiveModel::Validations::UrlValidator in 'validates' statement.
Make use of the options attribute of the parent class ActiveModel::EachValidator.
Add more options: allow_nil, allow_blank, message.
Renamed 'protocols' option to 'schemes' to match the option naming from UrlValidator.

ci/yaml: add version info to changes only/except

See merge request gitlab-org/gitlab-ce!24062

Clarify "Shell commands" link title in style guide doc

See merge request gitlab-org/gitlab-ce!27241