fix(backup): reimport the postgres dump on restore (restore was a no-op)

The recipe dumped the DB on backup but shipped NO backupbot.restore.post-hook, and
archived the whole live PGDATA dir — so a restore extracted files under the running
postgres without reloading them, silently keeping the un-restored (live) state. A
restored backup therefore lost all data written since the snapshot.

Switch to the coop-cloud /pg_backup.sh convention (as matrix-synapse): backup =
pg_dump|gzip -> backup.sql; restore = terminate connections, FORCE-drop, recreate,
reimport the dump deterministically. Archive just backup.sql, not the whole PGDATA dir.

compose.yml

@@ -2,7 +2,7 @@ version: "3.8"
 
 services:
   app:
-    image: mattermost/mattermost-team-edition:11.7.5
+    image: mattermost/mattermost-team-edition:10.11.18
     environment:
       - TZ
       - MM_SQLSETTINGS_DRIVERNAME=postgres
@@ -28,7 +28,7 @@ services:
         - "traefik.http.routers.${STACK_NAME}.middlewares=${STACK_NAME}-redirect"
         - "traefik.http.middlewares.${STACK_NAME}-redirect.headers.SSLForceHost=true"
         - "traefik.http.middlewares.${STACK_NAME}-redirect.headers.SSLHost=${DOMAIN}"
-        - "coop-cloud.${STACK_NAME}.version=2.1.12+10.11.20"
+        - "coop-cloud.${STACK_NAME}.version=2.1.10+10.11.18"
         - "backupbot.backup=true"
         - "backupbot.backup.path=/mattermost,/etc/ssl"
     configs: