make everything more modular + basic kitagawa config using gnome

modules/display-managers/gdm.nix

@@ -0,0 +1,7 @@
+{
+  config,
+  pkgs,
+  ...
+}: {
+  services.displayManager.gdm.enable = true;
+}

modules/display-managers/sddm.nix

@@ -0,0 +1,18 @@
+{
+  config,
+  pkgs,
+  ...
+}: {
+  services.displayManager.sddm = {
+    enable = true;
+    theme = "breeze";
+    wayland.enable = true;
+    enableHidpi = true;
+    settings = {
+      Autologin = {
+        Session = "plasma.desktop";
+        User = "grey";
+      };
+    };
+  };
+}