In a previous attempt (rolled back in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16021) we tried
to migrate `issues.closed_at` from timestamp to timestamptz using a
regular migration. This has a bad impact on GitLab.com and as such was
rolled back.

This commit re-implements the original migrations using generic
background migrations, allowing us to still migrate the data in a single
release but without a negative impact on availability.

To ensure the database schema is up to date the background migrations
are performed inline in development and test environments. We also make
sure to not migrate that that doesn't need migrating in the first place
or has already been migrated.

Fix user membership destroy relation

Closes #40053

See merge request gitlab-org/gitlab-ce!15970

QA: Add a scenario for adding a deploy key

See merge request gitlab-org/gitlab-ce!16096

Ignore "lost+found" folder during backup on a volume

Closes #22672 and #17574

See merge request gitlab-org/gitlab-ce!16036

Update prometheus gem to version that publishes +Inf bucket in accordance with Prometheus docs.

See merge request gitlab-org/gitlab-ce!16175

Forking a project to a namespace with lower visibility

Closes #40022

See merge request gitlab-org/gitlab-ce!16050

everything in the scenario without a before block.

Clears visual token on second backspace

Closes #38596

See merge request gitlab-org/gitlab-ce!15348

Merge branch '39289-local-schema-rb-automatically-reverts-datetime-to-datetime_with_timezone-after-migrations' into 'master'

Prevent schema.rb reverting from datetime_with_timezone to datetime

Closes #39289

See merge request gitlab-org/gitlab-ce!14956

Resolve "Rename "Browse file" inputs to "Choose file""

Closes #40780

See merge request gitlab-org/gitlab-ce!16092

Fix breadcrumbs in User Settings

Closes #40274

See merge request gitlab-org/gitlab-ce!16172

Rename asset sync related AWS variables

See merge request gitlab-org/gitlab-ce!16154

Closes #40274

Fix 404 error after a user edits an issue description and solves the reCAPTCHA

Closes #41445

See merge request gitlab-org/gitlab-ce!16167

Documenting that resolved JIRA tickets are not automatically transitioned

See merge request gitlab-org/gitlab-ce!16162

When editing an issue, use the PUT method instead of POST to avoid
a 404 after solving the reCAPTCHA.

Closes #41445

Adjust content width for User Settings, GPG Keys

See merge request gitlab-org/gitlab-ce!16093

Keep typographic hierarchy in User Settings

See merge request gitlab-org/gitlab-ce!16090

Fix links to old commits in merge request comments

Closes #41492

See merge request gitlab-org/gitlab-ce!16152

Add pause/resume button to project runners

Closes #20035

See merge request gitlab-org/gitlab-ce!16032

Move encoding methods to the more general EncodingHelper

Closes gitaly#847

See merge request gitlab-org/gitlab-ce!16137

In this case the project will get the minimum between both
visibilities.

If that visibility is restricted, then a lower level will be picked.

- Authentication log
- Notifications

Resolve "First request after GDK server started is slow"

Closes #38930

See merge request gitlab-org/gitlab-ce!16153

Fixed abuse reports link url

See merge request gitlab-org/gitlab-ce!16068

Bumped mysql2 gem version from 0.4.5 to 0.4.10.

See merge request gitlab-org/gitlab-ce!16034

Resolve "Webpack Roadmap"

Closes #38869

See merge request gitlab-org/gitlab-ce!16076