Clean stale background migration jobs
In !24135 (merged), we
reverted the problematic ActivatePrometheusServicesForSharedClusterApplications
background
migration, but the migration only dropped jobs that were in the
background_migration
Sidekiq queue. There may be more jobs in the
Sidekiq scheduled or retry sets, so we need to clear those too.
Closes https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/9160
Edited by Yorick Peterse