Online GC: Lock contention on manifest deletes
Context
Found to be the cause for a severity3 production incident gitlab-com/gl-infra/production#7465 (closed).
Problem
During the investigation of the incident above, we detected many manifest deletions timing out on the DB server side due to a ShareLock contention. The root cause for this is still unknown and requires investigation.
See #732 (comment 1030488395) for more details and sample logs.