praefect: Support object pool disconnection in Praefect replicator

When a secondary repository replica in Praefect is out of sync with the primary replica, Praefect creates a replication job that performs the ReplicateRepository RPC to replicate the up-to-date primary onto the secondary. As part of this operation the replicator also checks if the source repository is linked to an object pool and if so links the target to the matching object pool on the secondary.

If the primary is not linked to an object pool and the secondary is linked to an object pool, no change is made to the target repository object pool relationship and the replication job continues normally. This is problematic because it allows secondary repositories to diverge from the primary. Also if the repository attempts to link to a new object pool via the LinkRepositoryToObjectPool RPC, the secondary repositories will always fail due to already being linked to an object pool.

To prevent this from occurring, the target repository should also perform the DisconnectGitAlternates RPC if it is determined that the source repository is not linked to an object pool. This change updates the Praefect replicator to perform object pool disconnects to ensure the target repository remains consistent with the source.

Related: #5679 (closed)