Handle KRaft snapshots in dual-write mode

While the KRaft controller is making writes back to ZK during the migration, we need to handle the case when a snapshot is loaded. This can happen for a number of reasons in KRaft.

The difficulty here is we will need to compare the loaded snapshot with the entire state in ZK. Most likely, this will be a very expensive operation.

Without this, dual-write mode cannot safely tolerate a snapshot being loaded, so marking this as a 3.5 blocker.