Tailscale: Enable client routing features to enable exit nodes

modules/services/tailscale.nix

@@ -2,6 +2,8 @@
   flake.modules.nixos.tailscale = {
     services.tailscale = {
       enable = true;
+      # required for using exit nodes
+      useRoutingFeatures = "client";
     };
   };
 }