postgres: Add pgBackRest integration

This serves to supersede rsnapshot, which has severe performance issues.

postgres/tasks/main.yml

@@ -102,6 +102,8 @@
           value: >-
             run-parts --report --arg=%p --arg=%f --arg=pgbackrest
             /etc/postgresql/wal-archive
+      notify:
+        - Restart Postgres
 
 - name: Configure Commvault backup compatibility
   when: postgres_commvault_compat