Gossipsub peer exchange

[jm-clius]

Background

GossipSub Peer Exchange (PX) is a GossipSub v1.1 mechanism whereby a pruning peer may provide a pruned peer with a set of alternative peers where it can connect to reform its mesh. This is a very suitable mechanism to gradually discover more peers from an initial connection to a small set of bootstrap peers.

Acceptance criteria

Gossipsub Peer Exchange has now been implemented in nim-libp2p. The underlying submodule should now be updated for nwaku, peer exchange enabled (or it least made configurable on a nwaku level) and peers discovered in this way handled appropriately (e.g. connected to, or added to the nwaku peer store).