Support Postgres 15+

[jrafanie]

Postgres 13 is EOL Nov 25, 2025

High level: We need to get HA support which primarily involves repmgr compiled and built against postgres 15. We also need to test logical replication for region support. Both would need to be tested on appliances and new rpms delivered for upgrades.

We're using repmgr 5.2.1, implemented in:
ManageIQ/manageiq-rpm_build#309
ManageIQ/manageiq-rpm_build#341
ManageIQ/manageiq-rpm_build#443

It's currently at version 5.4.1 and supports postgres 16: https://www.repmgr.org/docs/current/index.html

5.3.0 supports PG 14 https://www.repmgr.org/docs/current/release-5.3.0.html
5.3.3 supports PG 15 https://www.repmgr.org/docs/current/release-5.3.3.html