Add sshd module

modules/sshd.nix

@@ -0,0 +1,16 @@
+_: {
+  services.openssh = {
+    enable = true;
+    settings.PasswordAuthentication = false;
+    settings.KbdInteractiveAuthentication = false;
+    hostKeys = [
+      # Generate a key if it's missing, which is normal at first boot, but can
+      # also be a TPM failure for PCs with a TPM.
+      # Do not generate an RSA key.
+      {
+        path = "/etc/ssh/ssh_host_ed25519_key";
+        type = "ed25519";
+      }
+    ];
+  };
+}