pg_createsubscriber: Add -R publications option.

pg_createsubscriber: Add -R publications option.

This patch introduces a new '-R'/'--remove' option in the
'pg_createsubscriber' utility to specify the object types to be removed
from the subscriber. Currently, we add support to specify 'publications'
as an object type. In the future, other object types like failover-slots
could be added.

This feature allows optionally to remove publications on the subscriber
that were replicated from the primary server (before running this tool)
during physical replication. Users may want to retain these publications
in case they want some pre-existing subscribers to point to the newly
created subscriber.

Author: Shubham Khanna 
Reviewed-by: Peter Smith 
Reviewed-by: David G. Johnston 
Reviewed-by: Euler Taveira 
Reviewed-by: Zhijie Hou 
Reviewed-by: vignesh C 
Reviewed-by: Nisha Moond 
Reviewed-by: Amit Kapila 
Discussion: https://postgr.es/m/CAHv8RjL4OvoYafofTb_U_JD5HuyoNowBoGpMfnEbhDSENA74Kg@mail.gmail.com