network-libp2p: improve reachability of nodes behind a NAT

[vlvrd]

Original issue description:
When a peer is behind a reverse proxy / load balancer, the server's loopback IF or private IP is reflected as the source IP address, which means that the Identify protocol isn't relaying the correct IP for NAT transversal. This is a documented libp2p issue and support for the Proxy protocol has been requested.

The goal of this issue is to improve the reachability of nodes that are behind a NAT (load balancer, reverse proxy, etc). Initially the idea to address this is by improving the reflected source IP of the node such that peers dial an address that is reachable from the public internet. The libp2p feature request to implement the Proxy Protocol that could improve the reachability was marked as not planned.

Now with the recent release of AutoNAT V2 (libp2p/rust-libp2p#5526) combined with the Circuit Relays protocol, is meant to be the next proposal to improve this reachability.

Tasks:

• Update the AutoNAT V1 in the root NetworkBehaviour to AutoNAT V2 (PR network-libp2p: Migrate AutoNAT v1 protocol to v2 #2955)
• Add the Circuit Relay protocol to the root NetworkBehaviour