add grub/systemd to common top level

common/boot/systemd.nix

@@ -0,0 +1,28 @@
+{
+  custom_config_key,
+  config,
+  lib,
+  ...
+}:
+let
+  cfg_path = "${custom_config_key}".boot.systemd;
+  cfg = config.${cfg_path};
+in
+with lib;
+{
+  options.${cfg_path} = {
+    enable = mkEnableOption "Systemd bootloader";
+  };
+  config = mkIf cfg.enable {
+    boot.loader = {
+      systemd-boot = {
+        enable = true;
+        consoleMode = "keep";
+      };
+      timeout = 5;
+      efi = {
+        canTouchEfiVariables = true;
+      };
+    };
+  };
+}