Doc: Add documentation for sequence synchronization.

Doc: Add documentation for sequence synchronization.

Add documentation describing sequence synchronization support in logical
replication. It explains how sequence changes are synchronized from the
publisher to the subscriber, the configuration requirements, and provide
examples illustrating setup and usage.

Additionally, document the pg_get_sequence_data() function, which allows
users to query sequence details on the publisher to determine when to
refresh corresponding sequences on the subscriber.

Author: Vignesh C <vignesh21@gmail.com>
Reviewed-by: Peter Smith <smithpb2250@gmail.com>
Reviewed-by: shveta malik <shveta.malik@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CAA4eK1LC+KJiAkSrpE_NwvNdidw9F2os7GERUeSxSKv71gXysQ@mail.gmail.com