postgres: Add pgBackRest integration

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

postgres/defaults/main.yml

@@ -2,3 +2,17 @@
 
 postgres_pgdg_repo: false
 postgres_rsnapshot: false
+postgres_commvault_compat: false
+postgres_pgbackrest: false
+postgres_wal_archive: "{{ postgres_commvault_compat or postgres_pgbackrest }}"
+
+pgbackrest_retention_diff: 7
+pgbackrest_retention_full: 2
+pgbackrest_frequently_minute: "*/15"
+
+postgres_versions_debian:
+  buster: "11"
+  bullseye: "13"
+  bookworm: "14"
+
+postgres_version: "{{ postgres_versions_debian[ansible_distribution_release] }}"