pgsql: Add GUC option to control maximum active replication origins.

Add GUC option to control maximum active replication origins.

This commit introduces a new GUC option max_active_replication_origins
to control the maximum number of active replication
origins. Previously, this was controlled by
'max_replication_slots'. Having a separate GUC option provides better
flexibility for setting up subscribers, as they may not require
replication slots (for cascading replication) but always require
replication origins.

Author: Euler Taveira <euler(at)eulerto(dot)com>
Reviewed-by: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Reviewed-by: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Reviewed-by: vignesh C <vignesh21(at)gmail(dot)com>
Discussion: https://postgr.es/m/b81db436-8262-4575-b7c4-bc0c1551000b@app.fastmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/04ff636cbce4b91fba1f334e1bc0dc88686e7b2d

Modified Files
--------------
doc/src/sgml/config.sgml | 26 +++------
doc/src/sgml/logical-replication.sgml | 10 ++--
doc/src/sgml/ref/pg_createsubscriber.sgml | 2 +-
src/backend/replication/logical/launcher.c | 6 +-
src/backend/replication/logical/origin.c | 66 ++++++++++------------
src/backend/utils/misc/guc_tables.c | 12 ++++
src/backend/utils/misc/postgresql.conf.sample | 2 +
src/bin/pg_basebackup/pg_createsubscriber.c | 20 +++----
src/bin/pg_basebackup/t/040_pg_createsubscriber.pl | 4 +-
src/bin/pg_upgrade/check.c | 18 +++---
src/bin/pg_upgrade/t/004_subscription.pl | 17 +++---
src/include/replication/origin.h | 3 +
12 files changed, 93 insertions(+), 93 deletions(-)