Obtain latency between discovered peers

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Starting point to investigate on is https://docs.libp2p.io/concepts/protocols/#ping

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See also:

• https://pkg.go.dev/github.com/libp2p/go-libp2p-kad-dht@v0.15.0/pb#ProtocolMessenger.GetClosestPeers
• https://github.com/libp2p/go-libp2p-kad-dht/blob/master/metrics/metrics.go
• https://github.com/libp2p/go-libp2p-kad-dht/blob/master/fullrt/dht.go#L397
• https://github.com/libp2p/go-libp2p-kad-dht/blob/master/lookup.go#L19