Backports EE mirror stuck handling feature…

See merge request !13627

Use grpc 1.4.5

Closes gitaly#468

See merge request !13597

Backports EE mirror stuck handling feature (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2628) to CE

Fixed height of group share dropdown

Closes gitlab-ee#3149

See merge request !13505

Improve migrations / background migrations testing strategy

Closes #36303

See merge request !13589

Resolve "Deleting of a GitLab Pages project results in "`PagesWorker.perform_in` cannot be called inside a transaction""

Closes #35072

See merge request !13631

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/3149

Fix project import to group when there are project milestones

Closes #35580

See merge request !13482

expose Referable#non_referable_inspect

See merge request !13613

Fix project templates and add docs

Closes #36492

See merge request !13563

`migrate!` helper triggers a migration that is under the test, so we
need to revert it before each subsequent example. This means that we
need to place it in `before(:each, :migration)` hook.

We still want to migrate everything up *after* each *context*, so in
otherwords we need to place migrate up helper in `before(:context,
:migration)`.

Fixed collapsed sidebar not showing fly-out menu

See merge request !13622

Upgrade grape to 1.0

Closes #36588

See merge request !13609

Fix help page version image spec

Closes #36592

See merge request !13605

Fix milestone sidebar collapse button

Closes #36453

See merge request !13620

The link pointed to the wrong page, this is corrected by both writing
the documentation and linking to that instead.

(internal)
Reference: https://gitlab.slack.com/archives/C0NFPSFA8/p1502791719000238

The params were not getting a value other than `project_templates:"on"`
so the backend wasn't sure what template to use.

Fixes gitlab-org/gitlab-ce#36492

Add reserved names to docs

See merge request !13583

Main feature was the deprication of the Hashie stuff, so the access by
calling keys as method is gone now.

Only create commit GPG signature when necessary

See merge request !13561

Change 'This issue is not confidential' to 'Not confidential'

See merge request !13607

Repo editor with flex layout

See merge request !13571

Fix commit list request appending 40 to offset

Closes #36569 and #36563

See merge request !13603