borg_client: run compact after pruning on borg 1.2

Only doing this on the Hetzner storage box for now; waiting for
rsync.net to upgrade to borg 1.2 so we can enable it there too.

roles/borg_client/defaults/main.yml

@@ -4,7 +4,9 @@ backup_hosts:
     dir: "~/repo"
     suffix: ""
     borg_cmd: "borg"
+    compact_after_prune: true
   - host: "ssh://zh1905@zh1905.rsync.net:22"
     dir: "~/backup/{{ inventory_hostname }}"
     suffix: "-offsite"
     borg_cmd: "borg --remote-path=borg1"
+    compact_after_prune: false # not upgraded to borg 1.2 yet

roles/borg_client/templates/borg-backup.sh.j2

@@ -88,4 +88,9 @@ fi
     -e "$backup_mountdir/var/lib/archbuilddest" \
     -e "$backup_mountdir/var/lib/docker" \
     {{ item['host'] }}/{{ item['dir'] }}::$(date "+%Y%m%d-%H%M%S") "$backup_mountdir"
+
 {{ item['borg_cmd'] }} prune -v {{ item['host'] }}/{{ item['dir'] }} --keep-daily=7 --keep-weekly=4 --keep-monthly=6
+
+{% if item['compact_after_prune'] %}
+{{ item['borg_cmd'] }} compact -v {{ item['host'] }}/{{ item['dir'] }}
+{% endif %}