This converts the MergeRequestCleanupRefsWorker to be a limited
capacity worker.

The ScheduleMergeRequestCleanupRefsWorker will still be enqueuing
jobs but it'll be based on capacity. If there's no capacity then
no new jobs will be enqueued.

For now, we are capping it at 4 jobs at a time. This will be later
on be configurable.

This is still behind the merge_request_refs_cleanup feature flag
so we can easily turn it off on production while testing.

Changelog: changed

Respect absolute date user setting in MR widget

See merge request gitlab-org/gitlab!66045

Display full name of fork namespace

See merge request gitlab-org/gitlab!65203

Add "empty" scenario and refactor viewers spec

See merge request gitlab-org/gitlab!66009

Remove codequality_mr_diff_annotations flag

See merge request gitlab-org/gitlab!65960

Quarantine broken QA test

See merge request gitlab-org/gitlab!66125

Change default metric definition template category to Optional

See merge request gitlab-org/gitlab!66076

Add trial suffix to can_extend and can_reactivate methods in the Namespace class

See merge request gitlab-org/gitlab!66061

Update localTimeAgo to accept Arrays and NodeList

See merge request gitlab-org/gitlab!65851

Add Cluster Image Scanning to vuln scan details

See merge request gitlab-org/gitlab!65962

Fix escaped chars in remove and delete modals

See merge request gitlab-org/gitlab!65990

Merge branch '335269-snowflake-data-warehouse-downstream-impact-due-to-db_structure-changes' into 'master'

Resolve "Snowflake dwh impact due to db_structure changes"

See merge request gitlab-org/gitlab!65537

Exclude flaky example from review-qa-smoke job

See merge request gitlab-org/gitlab!65705

Upgrade GitLab Pages to 1.41.0

See merge request gitlab-org/gitlab!66033

Minor refinements and enhancements to Vale and Markdownlint rules

See merge request gitlab-org/gitlab!66035

The fix is not as simple as first thought.

Document lazy failovers in Praefect

See merge request gitlab-org/gitlab!62704

Update feature specs for issues refactor

See merge request gitlab-org/gitlab!66080

End to end test for branch switcher fetch policy

See merge request gitlab-org/gitlab!63811

Add test case parsing limit and node limit

See merge request gitlab-org/gitlab!65872

Add new filtered search to issue boards [RUN ALL RSPEC] [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!61752

Replaced quotes with bold

See merge request gitlab-org/gitlab!66105

Add link to AuditEvent instrumentation

See merge request gitlab-org/gitlab!66085

Rename project / group removal to deletion

See merge request gitlab-org/gitlab!66064

Rename License.usage_ping to License.customer_service_enabled

See merge request gitlab-org/gitlab!65834

Document :exclude tag in E2E testing docs

See merge request gitlab-org/gitlab!66110

Automatically manage webdrivers via webdrivers gem

See merge request gitlab-org/gitlab!66057

Fix duplicate tests in Groups API spec

See merge request gitlab-org/gitlab!65823

Add descriptions for HealthStatus

See merge request gitlab-org/gitlab!65886

Increment DAST_VERSION in on-demand DAST template

See merge request gitlab-org/gitlab!65218

See https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/947

Ensure pages visibility levels are correct

See merge request gitlab-org/gitlab!65723