pgsql: Doc: Add more links in logical replication pages.

Doc: Add more links in logical replication pages.

The logical replication pages in the docs mostly have links to
corresponding pub/sub commands whenever they are mentioned, but there were
some omissions. This patch adds the missing links.

Author: Peter Smith
Reviewed-by: Vignesh C, Amit Kapila
Discussion:
https://www.postgresql.org/message-id/flat/CAHut%2BPu2S4RdzYKR7H5_E7QYWyq5hB0hL4EFrYbP91Qso62jeg%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/536f410111fc9b4a9e052ac53826f479acfca2f5

Modified Files
--------------
doc/src/sgml/logical-replication.sgml    | 20 +++++++++++++-------
doc/src/sgml/ref/alter_publication.sgml  |  3 ++-
doc/src/sgml/ref/alter_subscription.sgml | 23 ++++++++++++-----------
doc/src/sgml/ref/drop_subscription.sgml  |  8 +++++---
4 files changed, 32 insertions(+), 22 deletions(-)