Add UPnP support for Lighthouse (#1587)

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

## Issue Addressed

#927 

## Proposed Changes

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

## Additional Info



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

beacon_node/network/src/lib.rs

@@ -8,6 +8,7 @@ pub mod service;
 mod attestation_service;
 mod beacon_processor;
 mod metrics;
+mod nat;
 mod persisted_dht;
 mod router;
 mod sync;