Backport of gitlab-ee!6767

See merge request gitlab-org/gitlab-ce!21037

Resolve "Recover reverted fixes to Merge Request refactor regressions"

Closes #49242, #49343, #48876, #48877, #48817, #48602, and #49843

See merge request gitlab-org/gitlab-ce!20968

Add omnibus setting examples for standalone gitaly server

See merge request gitlab-org/gitlab-ce!21049

Resolve "System level labels UI broken"

Closes #48456

See merge request gitlab-org/gitlab-ce!21046

Avoid N+1 on MRs page when metrics merging date cannot be found

Closes #47613

See merge request gitlab-org/gitlab-ce!21053

Resolve "Frontend for clarifying the usefulness of the search bar"

Closes #36409

See merge request gitlab-org/gitlab-ce!20537

Fix typo and improve formatting

See merge request gitlab-org/gitlab-ce!21056

Update git rerere link in docs

See merge request gitlab-org/gitlab-ce!21060

The original link was moved.

Add documentation for setting up a user status

See merge request gitlab-org/gitlab-ce!21045

Send resize parameters for avatars

See merge request gitlab-org/gitlab-ce!20966

Update CreateItemDropdown class to allow the glDropdown filterRemote option

See merge request gitlab-org/gitlab-ce!21041

Resolve "Improve Auto DevOps settings flow for admin and project"

Closes #47156

See merge request gitlab-org/gitlab-ce!20946

Add support for Bitbucket Server imports

Closes #25393

See merge request gitlab-org/gitlab-ce!20164

Resolve "Charts with long label appear oversized"

Closes #48419

See merge request gitlab-org/gitlab-ce!20866

Revert "Merge branch 'bvl-instance-stats-default' into 'master'"

See merge request gitlab-org/gitlab-ce!21054

Persist 'auto devops' banner dismissal globally

Closes #48657

See merge request gitlab-org/gitlab-ce!20540

Respond to DB health in background migrations

See merge request gitlab-org/gitlab-ce!20720

Retrieve merge request closing issues from database cache

Closes #44821

See merge request gitlab-org/gitlab-ce!20911

This reverts merge request !21044

Resolve "Increase width of left column in reports modal"

Closes #49835

See merge request gitlab-org/gitlab-ce!21048

Allow multiple JIRA transitions id split by comma or semicolon

Closes #43602

See merge request gitlab-org/gitlab-ce!20939

The background migration interval has been reduced from 5 minutes to 2
minutes, so we have to adjust this migration accordingly.

This changes the BackgroundMigration worker so it checks for the health
of the DB before performing a background migration. This in turn allows
us to reduce the minimum interval, without having to worry about blowing
things up if we schedule too many migrations.

In this setup, the BackgroundMigration worker will reschedule jobs as
long as the database is considered to be in an unhealthy state. Once the
database has recovered, the migration can be performed.

To determine if the database is in a healthy state, we look at the
replication lag of any replication slots defined on the primary. If the
lag is deemed to great (100 MB by default) for too many slots, the
migration is rescheduled for a later point in time.

The health checking code is hidden behind a feature flag, allowing us to
disable it if necessary.

Hide instance statistics by default

Closes #50000

See merge request gitlab-org/gitlab-ce!21044

Making the migrations and the default do the right thing in the first
place. This makes 20180806094307 a no-op.

Add a generic more CSS class to render expandable reports correctly

See merge request gitlab-org/gitlab-ce!21014