peer Registration Race when client connects to the signal server

[braginini]

What?
Due to the async nature of gRPC bi-directional streams, the client gets successfully connected to the stream before the Signal server registers it in the registry. Therefore signal/client.WaitConnected() returns before the peer was registered.
This is visible in the test environments when signal and peers are "close", not likely to happen in the production scenario.

Why?
A peer has to start communication with other peers only when it has been registered therefore signal/client.WaitConnected() should unblock when the peer has been actually registered on signal

How?
We could introduce additional methods to register peer on signal or use meta headers of gRPC on ConnectStream