steam mod, move adwaita to homeModules

nixosModules/allowed-unfree-list.nix

@@ -0,0 +1,15 @@
+{ lib, config, ... }:
+{
+  options.allowedUnfreePackages = lib.mkOption {
+    type = lib.types.listOf lib.types.str;
+    default = [ ];
+    example = [ "steam" ];
+  };
+
+  config = {
+    nixpkgs.config = {
+      # https://github.com/NixOS/nixpkgs/issues/197325#issuecomment-1579420085
+      allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) config.allowedUnfreePackages;
+    };
+  };
+}