Gamemode & Steam Fix and Add Gamescope

- Move gamemode and steam to system packages
- Add gamescope to user packages

system/utilities/gaming.nix

@@ -0,0 +1,15 @@
+{ config, lib, pkgs, ... }:
+
+{
+  programs.gamemode = {
+    enable = true;
+    # settings = {};
+    # enableRenice = true;
+  };
+
+  programs.steam = {
+    enable = true;
+    remotePlay.openFirewall = true;
+    gamescopeSession.enable = true;
+  };
+}