Fix errors when deleting a forked project

Closes #39196

See merge request gitlab-org/gitlab-ce!14916

Use variable for mobile breadcrumbs padding

Closes #38156

See merge request gitlab-org/gitlab-ce!14904

The problem would occur when the `ForkedProjectLink` was deleted, but
the `ForkNetworkMember` was not. The delete would be rolled back and
retried.

But the error would not be saved because `Project#forked?`
would still be true, because the `ForkNetworkMember` exists. But the
`Project#forked_project_link` would be `nil`. So the validation for
the visibility level would fail.

Prevent creating multiple ApplicationSetting by forcing it to always have id=1

Closes #34728

See merge request gitlab-org/gitlab-ce!14718

Merge branch '39181-gitlab-backgroundmigration-deserializemergerequestdiffsandcommits-error-nomethoderror-undefined-method-map-for-nil-nilclass' into 'master'

Resolve "Gitlab::BackgroundMigration::DeserializeMergeRequestDiffsAndCommits::Error: #<NoMethodError: undefined method `map' for nil:NilClass"

Closes #39181

See merge request gitlab-org/gitlab-ce!14907

Adds collapsible sections in cluster page

See merge request gitlab-org/gitlab-ce!14890

This is already handled for diffs, but not commits.

Allow testing on Gitaly call count

See merge request gitlab-org/gitlab-ce!14837

Clarify how to resume GitHub import on docs

See merge request gitlab-org/gitlab-ce!14905

Bump Git version to 2.13.6

See merge request gitlab-org/gitlab-ce!14906

Make the circuitbreaker configurable at runtime

See merge request gitlab-org/gitlab-ce!14842

Show collapsible tree on the project show page

Closes #30343

See merge request gitlab-org/gitlab-ce!14055

Instead of from the configuration file

Add ability to pass class name to spriteIcon helper

Closes #39079

See merge request gitlab-org/gitlab-ce!14855

Fix link to "Job Permissions"

See merge request gitlab-org/gitlab-ce!14896

Remove extra border radius when editing a file

Closes #37978

See merge request gitlab-org/gitlab-ce!14803

Update new project docs

See merge request gitlab-org/gitlab-ce!14893

39035 Move GitLab export option to top of import list when creating a new project

Closes #39035

See merge request gitlab-org/gitlab-ce!14830

Remove banner from pipelines page

Closes #38641, #39051, and #38827

See merge request gitlab-org/gitlab-ce!14849

Remove "boards" from TOP_LEVEL_ROUTES

Closes #39073

See merge request gitlab-org/gitlab-ce!14861

Adds requirements that supports anything in sha params

Closes #26561 and #2709

See merge request gitlab-org/gitlab-ce!14462

Resolve "GitlabUsagePingWorker is not running on GitLab.com"

See merge request gitlab-org/gitlab-ce!14867

Add Performance category to the changelog

Closes #36417

See merge request gitlab-org/gitlab-ce!14865

Upgrading Monaco

Closes #38607

See merge request gitlab-org/gitlab-ce!14629

Add Test::Integration::Mattermost

See merge request gitlab-org/gitlab-ce!14818

Add Gitlab::Git::Env.to_env_hash

See merge request gitlab-org/gitlab-ce!14841

update postgresql requirements

See merge request gitlab-org/gitlab-ce!14885

Resolve "Remove "Build failed" TODO if it has been auto-retried"

Closes #38236

See merge request gitlab-org/gitlab-ce!14869