add SSH hardening and fail2ban to common services

modules/common/services.nix

@@ -1,6 +1,12 @@
 { config, lib, pkgs, ... }:
 
 {
-  services.openssh.enable = true;
+  services.openssh = {
-  services.openssh.permitRootLogin = "no";
+    enable = true;
+    permitRootLogin = "no";
+    passwordAuthentication = false;
+    startWhenNeeded = true;
+  };
+
+  services.fail2ban.enable = true;
 }