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

The db service dumped the DB on backup (pg_dump pre-hook) but shipped no
restore hook, and a file-level restore does not reload into the running
postgres, so a restored backup silently kept the live (un-restored) state.
Add pg_backup.sh (backup=pg_dump|gzip into the postgresql_data volume;
restore=terminate conns + DROP DATABASE WITH FORCE + createdb + reimport),
mount it via a config, and wire the backupbot backup/restore hooks. Same
fix as the immich / mattermost-lts / ghost recipes.

compose.yml

@@ -133,8 +133,8 @@ networks:
 configs:
   db_entrypoint:
     name: ${STACK_NAME}_db_entrypoint_${DB_ENTRYPOINT_VERSION}
-    file: entrypoint.postgres.sh.tmpl
-    template_driver: golang
   pg_backup:
     name: ${STACK_NAME}_pg_backup_${PG_BACKUP_VERSION}
     file: pg_backup.sh
+    file: entrypoint.postgres.sh.tmpl
+    template_driver: golang