nixos/ripple-data-api: define group

required after #133166
untested, the module is broken by the removal of couchdb

nixos/modules/misc/ids.nix

@@ -218,7 +218,7 @@ in
       #unifi = 183; dynamically allocated as of 2021-09-17
       uptimed = 184;
       zope2 = 185;
-      ripple-data-api = 186;
+      #ripple-data-api = 186; dynamically allocated as of 2021-09-17
       mediatomb = 187;
       #rdnssd = 188; #dynamically allocated as of 2021-09-18
       ihaskell = 189;

nixos/modules/services/misc/ripple-data-api.nix

@@ -187,7 +187,9 @@ in {
 
     users.users.ripple-data-api =
       { description = "Ripple data api user";
-        uid = config.ids.uids.ripple-data-api;
+        isSystemUser = true;
+        group = "ripple-data-api";
       };
+    users.groups.ripple-data-api = {};
   };
 }