Added GDM

modules/greeter/gdm/default.nix

@@ -0,0 +1,25 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+with lib;
+let
+  cfg = config.modules.gdm;
+in
+{
+  options.modules.gdm = {
+    enable = mkEnableOption "gdm";
+  };
+
+  config = mkIf cfg.enable {
+    services.xserver = {
+      enable = true;
+      displayManager.gdm.enable = true;
+      displayManager.gdm.wayland = true;
+      libinput.enable = true;
+    };
+  };
+}