gitlab-ce: call PoolService::LinkRepositoryToPool prior to Repack / GarbageCollect on pool participant repos
Repositories that participate in a pool will have normal GC happening to them, called from Sidekiq. If the project is supposed to be in a pool but we somehow failed to establish the pool links on disk in Gitaly, this is a good time to re-establish them.
So if the repo belongs to a pool according to SQL, then call PoolService::LinkRepositoryToPool to re-establish the pool relation if necessary.
Pool repositories must be excluded from the garbage collection schedule. Pool repositories are the special repos that collect deduplicated objects. In the first iteration of object dedup, we must not run GC on them -- it would lead to data loss.