Support for streaming in transport

[appaquet]

Right now, transport only support message passing. In order to optimize chain bootstrapping, we need to be able to support streaming.

The way it could be implemented is to add an optional stream / sink field in InMessage / OutMessage.

In libp2p implementation, we need a new ProtcolHandler to support this. We use the "OneShot" handler that works for message passing, but not for streaming