Check protocols of relays found from kad provider

[dariusc93]

In the client example, we are using identify to check the peers protocols to determine if they support relay v2 HOP before adding it to the behaviour as a candidate, however we are not able to check when using kad providers to locate relays under /libp2p/relay, which creates a problem if a node only supports relay v2. What could be done here (which still serve as an example for implementation this behaviour) is that once we have the candidates we could send an event to the swarm to get the peer so we can trigger an identify event for them to check and determine if they support relay v2 and to filter out any that dont before selecting attempting any reservation.

Note:

1. Until swarm/: NetworkBehaviour/ConnectionHandler cross-communication libp2p/rust-libp2p#2680 is resolved, we will not be able to check the protocol directly in the behaviour.