feature(protonvpn): add protonvpn nix module

modules/nixos/protonvpn.nix

@@ -0,0 +1,9 @@
+{ config, lib, pkgs, ... }:
+
+{
+  networking.firewall.checkReversePath = false;
+  environment.systemPackages = with pkgs; [
+    wireguard-tools
+    protonvpn-gui
+  ];
+}