Enable feature update_all_mirrors_worker_rescheduling

Now that https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/11217 has been deployed, we can enable the update_all_mirrors_worker_rescheduling to switch to the new scheduling strategy.

This issue tracks the results and any observations we have.

Prep:

• Enable feature in staging with /chatops run feature set update_all_mirrors_worker_rescheduling true --staging (however there's no further benefit other than consistency with gprd because we don't do mirroring in gstg)

Steps:

• Enable feature with /chatops run feature set update_all_mirrors_worker_rescheduling true
• Check queuing behavior. Monitor for a while and make sure no alerts trigger.
• Review https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6678 by running another database checkup report after resetting statistics. Frequency of said query should have dropped significantly.
• Once proven stable, follow-up with https://gitlab.com/gitlab-org/gitlab-ee/issues/11499 to remove the feature flag.