Add a common function to generate the origin name.

Add a common function to generate the origin name.

Make a common replication origin name formatting function to replace
multiple snprintf() expressions. This also includes logic previously done
by ReplicationOriginNameForTablesync().

This makes the code to generate the origin name consistent among apply
worker and tablesync worker.

Author: Peter Smith
Reviewed-By: Aleksander Alekseev
Discussion: https://postgr.es/m/CAHut%2BPsa8hhfSE6ozUK-ih7GkQziAVAf4f3bqiXEj2nQiu-43g%40mail.gmail.com