nixos: services: migrate to 'ensureDBOwnership'

`ensurePermissions` is deprecated, and doesn't work on PostgreSQL 15.

modules/nixos/services/vikunja/default.nix

@@ -109,7 +109,7 @@ in
       ensureUsers = [
         {
           name = "vikunja";
-          ensurePermissions = { "DATABASE vikunja" = "ALL PRIVILEGES"; };
+          ensureDBOwnership = true;
         }
       ];
     };