Add mangohud automatically to all steam vulkan games

systems/modules/gaming.nix

@@ -1,13 +1,20 @@
 { config, pkgs, ... }:
 
 {
-  programs = {
-    steam.enable = true;
-    steam.remotePlay.openFirewall = true;
-    steam.localNetworkGameTransfers.openFirewall = true;
+  programs.steam = {
+    enable = true;
+    remotePlay.openFirewall = true;
+    localNetworkGameTransfers.openFirewall = true;
+    package = pkgs.steam.override {
+      extraEnv = {
+        MANGOHUD = "1";
+        WINE_VK_VULKAN_ONLY="1";
+      };
+    };
   };
 
   environment.systemPackages = [
     pkgs.heroic
+    pkgs.mangohud
   ];
 }