Fix CREATE SUBSCRIPTION failure when the publisher runs on pre-PG19.

Fix CREATE SUBSCRIPTION failure when the publisher runs on pre-PG19.

CREATE SUBSCRIPTION with copy_data=true and origin='none' previously
failed when the publisher was running a version earlier than PostgreSQL 19,
even though this combination should be supported.

The failure occurred because the command issued a query calling
pg_get_publication_sequences function on the publisher. That function
does not exist before PG19 and the query is only needed for logical
replication sequence synchronization, which is supported starting in PG19.

This commit fixes this issue by skipping that query when the
publisher runs a version earlier than PG19.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Shlok Kyal <shlok.kyal.oss@gmail.com>
Discussion: https://postgr.es/m/CAHGQGwEx4twHtJdiPWTyAXJhcBPLaH467SH2ajGSe-41m65giA@mail.gmail.com