Doc: Clarify that publication exclusions track table identity.

Doc: Clarify that publication exclusions track table identity.

The EXCEPT clause of a FOR ALL TABLES publication tracks each excluded
table by its identity rather than by name. As a result, renaming a table
or moving it to another schema with ALTER TABLE ... SET SCHEMA leaves the
exclusion in place, and the table stays excluded from the publication.

This behavior was not previously documented and could surprise users who
might reasonably expect a schema-qualified exclusion to apply only while
the table remains in that schema. Add a note to CREATE PUBLICATION to make
the behavior explicit.

Author: Peter Smith <smithpb2250@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CAHut+PvQ5BqnawCQd6r1tqqd+iAJC-CuRY8wscuXSrpHGUzofA@mail.gmail.com