more progress on custom options config

modules/components/boot-loaders/grub.nix

@@ -0,0 +1,8 @@
+{ inputs, self, ... }: {
+  flake.nixosModules.global = { pkgs, config, lib, ... }: {
+    boot.loader.grub = lib.mkIf (config.components.bootLoader == "grub") {
+      enable = true;
+      useOSProber = true;
+    };
+  };
+}