Fix duplicate key errors in PostDeployMigrateUserExternalMailData migration

Closes #38246

See merge request gitlab-org/gitlab-ce!14460

`email_provider` by default is NULL, and if a user had not logged the
value would remain NULL. Upgrading to GitLab 10.0 would lead to a
PG::UniqueViolation because the post-deploy migration would attempt
to reinsert the entry because the NULL comparison between
`users.email_provider` and `user_synced_attributes_metadata.email_provider`
would never match.

Closes #38246

Workaround for n+1 in Projects::TreeController#show

Closes #38171

See merge request gitlab-org/gitlab-ce!14455

Allow the git circuit breaker to correctly handle missing repository storages

Closes #36549

See merge request gitlab-org/gitlab-ce!14417

fix typo in icons section

See merge request gitlab-org/gitlab-ce!14444

Workaround for #38259

See merge request gitlab-org/gitlab-ce!14453

Inform user that current shared projects will remain shared

Closes #38220

See merge request gitlab-org/gitlab-ce!14441

See https://gitlab.com/gitlab-org/gitlab-ce/issues/38261

Removed old icons from project page

Closes #36567

See merge request gitlab-org/gitlab-ce!14185

Don't show %board-add-issues-modal if there's no project

See merge request gitlab-org/gitlab-ce!14442

Make branches page translatable

Closes #32797

See merge request gitlab-org/gitlab-ce!14221

Demonstrate <details> and <summary> tags in doc/user/markdown.md

See merge request gitlab-org/gitlab-ce!14247

Migrate Gitlab::Git::Repository#diff to Gitaly

Closes gitaly#524

See merge request gitlab-org/gitlab-ce!14251

Index projects on repository storage

See merge request gitlab-org/gitlab-ce!14414

Replace the 'project/shortcuts.feature' spinach test with an rspec analog

See merge request gitlab-org/gitlab-ce!14431

Fix `rake gitlab:incoming_email:check`

Closes #38197

See merge request gitlab-org/gitlab-ce!14423

Reserve refs/replace because `git-replace` is using it

Closes #38234

See merge request gitlab-org/gitlab-ce!14436

This is aligning with EE

Adds gitlab features and components to usage ping data.

Closes #33328

See merge request gitlab-org/gitlab-ce!14305

[ci skip]

Ensure that Blob.raw returns always returns a valid blob object

See merge request gitlab-org/gitlab-ce!14412

Add i18n support to pagination widget

See merge request gitlab-org/gitlab-ce!14407

Improve emoji menu rendering performance

Closes #36949

See merge request gitlab-org/gitlab-ce!14233

Fix bad link on GitLab Omnibus Helm chart page - docs

Closes #38016

See merge request gitlab-org/gitlab-ce!14346

Simplify a test

See merge request gitlab-org/gitlab-ce!14415

See:
* https://www.kernel.org/pub/software/scm/git/docs/git-replace.html
* https://git-scm.com/book/en/v2/Git-Tools-Replace

Resolve "Better SVG Usage in the Frontend"

Closes #36231

See merge request gitlab-org/gitlab-ce!13435

Add view replaced file link for image diffs

See merge request gitlab-org/gitlab-ce!14394

Do not clone the repo when running the review-docs jobs

See merge request gitlab-org/gitlab-ce!14420

Replace the 'project/service.feature' spinach test with an rspec analog

Closes #23036

See merge request gitlab-org/gitlab-ce!14432

Removed two legacy config options

See merge request gitlab-org/gitlab-ce!14425