Split up code to support server configuration

modules/ssh/default.nix

@@ -0,0 +1,20 @@
+{
+  lib,
+  config,
+  pkgs,
+  ...
+}:
+
+with lib;
+let
+  cfg = config.modules.ssh;
+in
+{
+  options.modules.ssh = {
+    enable = mkEnableOption "ssh";
+  };
+
+  config = mkIf cfg.enable {
+    services.openssh.enable = true;
+  };
+}