wm: Add module to set backlight

It's currently not used since it did not work as expected.

modules/wm/light.nix

@@ -0,0 +1,22 @@
+{ config, lib, pkgs, ... }:
+
+{
+  config.programs.light = { enable = true; };
+  config.services.actkbd = let light = "${pkgs.light}/bin/light";
+  in {
+    enable = true;
+    bindings = [
+      {
+        keys = [ 232 ];
+        events = [ "key" ];
+        command = "${light} -U 10";
+      }
+
+      {
+        keys = [ 233 ];
+        events = [ "key" ];
+        command = "${light} -A 10";
+      }
+    ];
+  };
+}