Mesh & Metadata Peers implementation

[thewoodfish]

So far to my understanding, we have one method of adding peers to our internal peer table: add_explicit_peer(). This does not allow me the flexibility of defining my mesh and gossip peer separately. If i keep a struct that does that, it is still futile because sending message to peers with gossip() does not take a list of multiaddresses or PeerIds to send to, it is high level. It just looks like floodsub to me. A lot like it. I think a function should be added to explicitly send a message to select PeerIds.

[thewoodfish]

add_explicit_peer() can be used to manage mesh peers. But for metadata peers, you can use a struct. Note that you must use the request-response behaviour to supplement gossipsub for maximum control and efficiency.