[nextcloud] enable postgresql backup

if we need to restore from backup this is necessary since db state from
zfs snapshots might be corrupted

machines/nextcloud/configuration.nix

@@ -31,6 +31,10 @@ with lib;
     lokiHost = "10.0.0.14";
   };
 
+  services.postgresqlBackup = {
+    enable = true;
+  };
+
   services.nextcloud = {
     enable = true;
     package = pkgs.nextcloud31;