postgres: Add Commvault backup compatibility

This slightly changes the default of the role by always installing postgresql-{{ postgres_version }} (and providing a sensible default for postgres_version), but this is usually the correct thing to do in Debian and a release upgrade requires manual work anyway.

mysql/defaults/main.yml

@@ -8,3 +8,6 @@ mysql_backup_user: "backup"
 mysql_backup_password: "{{ lookup('passwordstore', 'db/{{ ansible_hostname }}-mysql-backup create=true length=20') }}"
 
 mysql_rsnapshot: false
+# It is the admin’s responsibility to further configure binlogs, especially
+# purging them if required.
+mysql_enable_binlog: false