Answer with PEERS for GET_PEERS incoming message #28
Description
If we receive GET_PEERS message we should answer with PEERS message.
It happens here: https://github.com/astroband/astrocore/blob/master/src/actors/overlay_manager.rs#L93
We store known peers in this struct:
https://github.com/astroband/astrocore/blob/master/src/overlay/overlay_manager.rs#L41-L46