Wake up a subscription's replication worker processes after DDL.

Wake up a subscription's replication worker processes after DDL.

Waken related worker processes immediately at commit of a transaction
that has performed ALTER SUBSCRIPTION (including the RENAME and
OWNER variants).  This reduces the response time for such operations.
In the real world that might not be worth much, but it shaves several
seconds off the runtime for the subscription test suite.

In the case of PREPARE, we just throw away this notification state;
it doesn't seem worth the work to preserve it.  The workers will
still react after the eventual COMMIT PREPARED, but not as quickly.

Nathan Bossart

Discussion: https://postgr.es/m/20221122004119.GA132961@nathanxps13