Drop `exit == destination`

[richard-ramos]

Right now exit == destination exists only for gossipsub. Instead, we could define a new 'client' protocol for gossipsub: /gossipsub-relay/1.0.0. Gossipsub nodes would mount that protocol, and its sole job would be to receive a payload (an RPC protobuf message), and relay it.

Exit nodes could then dial any node that supports this protocol to relay gossipsub messages . Think of it as a way to expose gossipsub relay logic, from the perspective of gossipsub, it's just like if the message had arrived from another gossip peer, thus achieving the same result of providing client functionality to GossipSub, without having the client worry about dealing with gossipsub peers at all (no mesh, fanout, etc), as that would be the responsability of the destination node. It's like lightpush, but without calling publish to broadcast messages but instead injecting it into the message relaying logic

Task list

• Drop exit == destination code from entry_connection.nim, mix_protocol.nim and exit_layer.nim
• Create /gossipsub-relay/1.0.0 protocol in nim-libp2p
• Update POCs

[chaitanyaprem]

Maybe we should not drop this because while analysing how mix gets used in browser environment, it looks like moving to exit==destination would benefit Waku.

Please refer discussion here