added tailscale exit node module and enabled on server

modules/nix/tailscale-exit-node.nix

@@ -0,0 +1,12 @@
+{ ... }:
+
+{
+  services.tailscale = {
+    enable = true;
+
+    extraUpFlags = [
+      "--advertise-exit-node"
+      "--advertise-routes=192.168.2.0/24"
+    ];
+  };
+}