Merge branch '36630-activerecord-statementinvalid-pg-notnullviolation-error-null-value-in-column-a_mode-violates-not-null-constraint' into 'master'

Resolve "ActiveRecord::StatementInvalid: PG::NotNullViolation: ERROR:  null value in column "a_mode" violates not-null constraint"

Closes #36630

See merge request !13663

Describe the supported version of group-level variables API in document

Closes #36543

See merge request !13648

Update project_snippets.md

See merge request !13654

Guess the modes based on the following:

1. If the file didn't exist, it's zero.
2. If the diff contains 'Subproject commit', it might be a submodule, so 0600.
3. Otherwise, it's 0644.

This isn't perfect, but it doesn't have to be - it won't change file modes in
the repository.

Client Implementation: RefService::RefExists

Closes gitaly#452

See merge request !13528

Fix unnecessarily long gl.utils.backOff test

Closes #36648

See merge request !13651

Add support for i18n on Project Activity Page

Closes #32795

See merge request !13451

Setup settings properly

See merge request !13645

Don't escape html entities in InlineDiffMarkdownMarker

Closes #36041

See merge request !13553

Gitaly apply gitattributes

Closes gitaly#464

See merge request !13517

Updates for proper obj notation.

See merge request !13430

API: do not set rel="next" pagination header when no records found

Closes #36618

See merge request !13629

Fix external link to Composer website

Closes #36611

See merge request !13621

Make admin user actions dropdown consistent

See merge request !13630

Fixes the blown up emoji problem in notes

Closes #36448 and #36282

See merge request !13632

Properly explain when advanced Docker options were introduced

See merge request !13608

Docs: article - "Numerous undo possibilities in Git"

Closes gitlab-com/community-writers#40

See merge request !13513

And the link to the last page cannot be `page=0`.

Add specs that check the 'Link' header for the inclusion of:

 - rel="first"
 - rel="last"
 - rel="prev"
 - rel="next"

Fixes gitlab-org/gitlab-ce#36618

Related to gitlab-com/infrastructure#2532

Merge branch 'master' into 'docs-article-undo-things-in-git'

# Conflicts:
#   doc/articles/index.md

Move workflow/importing/ to user/project/import/

See merge request !13593

Prevent horizontal scrolling in new sidebar when collapsed

Closes #36608 and #36507

See merge request !13638

Allow all users to delete their account

Closes #36087

See merge request !13636

Backports EE mirror stuck handling feature…

See merge request !13627

Use grpc 1.4.5

Closes gitaly#468

See merge request !13597