repository: Sync Git alternates during replication

When a repository is replicated via the ReplicateRepository() RPC, object pool relationships are not recreated on the target repository. This change introduces Git altnernates file syncing between source and target repositories when the replicate_object_pool field is enabled for the RPC.

This operation is currently limited to linking the target repository to its object pool on the target storage. If the required target object pool does not exist, the target repository is not linked and replication continues as normal.