feat(ssh): add default module with enable+harden

modules/ssh/default.nix

@@ -0,0 +1,10 @@
+{ lib, ... }:
+
+{
+  imports = [ ./hardened-openssh.nix ];
+
+  config.services.openssh = {
+    enable = lib.mkDefault true;
+    harden = lib.mkDefault true;
+  };
+}