Add fast recovery option to recover_prepared_transaction

The normal implementation of `recover_prepared_transactions` does not block 2PCs, but can cause table bloat.

We sometimes get into trouble with `pg_dist_transaction` becoming very large and transaction recovery or autovacuum struggling to delete tuples fast enough to bring it down in size. It would be useful to have a fast way to reset pg_dist_transaction by adding an option to `recover_prepared_transactions` which:

1. blocks 2PCs
2. rolls pending prepared transactions on workers forward
3. truncates pg_dist_transaction

That way, we can quickly restore order in case of emergency.