Relevant EIPs:

• https://eips.ethereum.org/EIPS/eip-778

• https://eips.ethereum.org/EIPS/eip-868

• ENR class implemenation; creating initial ENR for Host; saving/loading from network.rlp ENR record for host #5537

• ENR Server - add enr-seq field to Pings and Pongs that we send; support answering ENRRequest packets.

• Updating Host's ENR (when we get new network config from the command line and when we get external IP from the incoming packet)

• ENR Client - change our discovery algorithm to query the nodes for ENR when we see they support it