Retrieval Peer Resolver

The peer resolver is a content routing interface to discover retrieval miners that have a given Piece.

It can be backed by both a local store of previous storage deals or by querying the chain.

// PeerResolver is an interface for looking up providers that may have a piece
type PeerResolver interface {
    GetPeers(payloadCID cid.Cid) ([]RetrievalPeer, error) // TODO: channel
}