modules: use user & group options

I've tried my best to locate all uses of hardcoded usernames, but its
not guaranteed that all have been found/fixed.

modules/lnd-rest-onion-service.nix

@@ -11,7 +11,7 @@ let
   lnd = config.services.lnd;
 
   bin = pkgs.writeScriptBin "lndconnect-rest-onion" ''
-    #!/usr/bin/env -S ${runAsUser} lnd ${pkgs.bash}/bin/bash
+    #!/usr/bin/env -S ${runAsUser} ${lnd.user} ${pkgs.bash}/bin/bash
 
     exec ${cfg.package}/bin/lndconnect \
      --host=$(cat ${config.nix-bitcoin.onionAddresses.dataDir}/lnd/lnd-rest) \