postgres: Add pgBackRest integration

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

postgres/tasks/pgbackrest.yml

@@ -56,12 +56,6 @@
       {% if item.sleep %}sleep $(($RANDOM \% 3600)) &&{% endif %}
       pgbackrest backup --stanza=main --type={{ item.type }}
   loop:
-    - name: frequently
-      weekday: "*"
-      hour: "*"
-      minute: "{{ pgbackrest_frequently_minute }}"
-      sleep: false
-      type: incr
     - name: daily
       weekday: 1-6
       hour: 3