feat(lib): Add mkEnableModule function

lib/module/default.nix

@@ -1,6 +1,16 @@
-{ lib, ... }:
+{ lib, namespace, ... }:
 with lib;
 rec {
+  ## Create a module option with only an enable option.
+  ## ```nix
+  ## options = lib.mkEnableModule "module-name"
+  ## ```
+  ##
+  #@ String
+  mkEnableModule = name: {
+    ${namespace}.${name}.enable = mkEnableModule "${name}";
+  };
+
   ## Create a NixOS module option.
   ##
   ## ```nix