Make sure validator discovery works with a delayed peer to validator mapping

Currently the implementation checks on connect of a peer if this peer is
a validator by asking the authority discovery. It can now happen that
the authority discovery is not yet aware that a given peer is an
authority. This can for example happen on start up of the node.

This pr changes the behavior, to make it possible to later associate a
peer to a validator id. Instead of just storing the connected
validators, we now store all connected peers with a vector of associated
validator ids. When we get a request to connect to a given given set of
validators, we start by checking the connected peers. If we didn't find
a validator id in the connected peers, we ask the authority discovery
for the peerid of a given authority id. When the returned peerid is part
of our connected peers set, we cache and return the authority id.