Add UPnP support for Lighthouse (#1587)

This commit was modified by Paul H whilst rebasing master onto
v0.3.0-staging

Adding UPnP support will help grow the DHT by allowing NAT traversal for peers with UPnP supported routers.

Using IGD library: https://docs.rs/igd/0.10.0/igd/

Adding the  the libp2p tcp port and discovery udp port. If this fails it simply logs the attempt and moves on

Co-authored-by: Age Manning <Age@AgeManning.com>

beacon_node/src/config.rs

@@ -507,7 +507,7 @@ pub fn set_network_config(
         config.enr_address = Some(resolved_addr);
     }
 
-    if cli_args.is_present("disable_enr_auto_update") {
+    if cli_args.is_present("disable-enr-auto-update") {
         config.discv5_config.enr_update = false;
     }
 
@@ -516,6 +516,10 @@ pub fn set_network_config(
         warn!(log, "Discovery is disabled. New peers will not be found");
     }
 
+    if cli_args.is_present("disable-upnp") {
+        config.upnp_enabled = false;
+    }
+
     Ok(())
 }