Skipping schema changes in publication

Hi,

This feature adds an option to skip changes of all tables in specified
schema while creating publication.
This feature is helpful for use cases where the user wants to
subscribe to all the changes except for the changes present in a few
schemas.
Ex:
CREATE PUBLICATION pub1 FOR ALL TABLES SKIP ALL TABLES IN SCHEMA s1,s2;
OR
ALTER PUBLICATION pub1 ADD SKIP ALL TABLES IN SCHEMA s1,s2;

A new column pnskip is added to table "pg_publication_namespace", to
maintain the schemas that the user wants to skip publishing through
the publication. Modified the output plugin (pgoutput) to skip
publishing the changes if the relation is part of skip schema
publication.
As a continuation to this, I will work on implementing skipping tables
from all tables in schema and skipping tables from all tables
publication.

Attached patch has the implementation for this.
This feature is for the pg16 version.
Thoughts?

Regards,
Vignesh