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

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

Trigger `project_update` system hook when archiving projects

See merge request gitlab-org/gitlab-ce!20995

Moves help_popover.vue to a common location

See merge request gitlab-org/gitlab-ce!21011

Keep Admin settings sections expanded after submitting form

See merge request gitlab-org/gitlab-ce!21040

Fix initialization of JS in pipeline `/failures` tab

Closes #49994

See merge request gitlab-org/gitlab-ce!21043

Use Gitaly 0.115.0

See merge request gitlab-org/gitlab-ce!21013

Changing the default in a new migration and updating the existing
values to change the defaults for instances already exposing the statistics.

Move xterm to a node dependency and remove it from vendor's folder

Closes #49741

See merge request gitlab-org/gitlab-ce!20588

Backport changes from gitlab-ee!6740

See merge request gitlab-org/gitlab-ce!21012

Revert some unneeded code changes from environment list

See merge request gitlab-org/gitlab-ce!21026

Port of protected environments frontend changes from EE to CE

See merge request gitlab-org/gitlab-ce!21018

Add group milestones to dashboard milestone page

Closes #35748

See merge request gitlab-org/gitlab-ce!20618

Resolve "Commit messages are no longer monospace, but still white-space: pre-wrap"

Closes #47548

See merge request gitlab-org/gitlab-ce!20988

Parse junit.xml.gz and calculate the difference between head and base

See merge request gitlab-org/gitlab-ce!20576

Rails5: update Rails5 lock for forgotten gem rouge

See merge request gitlab-org/gitlab-ce!21010

System hooks were not being triggered when projects were archived or
unarchived. Reuse the Projects::UpdateService to automatically
trigger system hooks and increase code reuse.