chain(penumbra): use gRPC for proof queries (#47)

This PR:

    makes the PenumbraChain provider rely on IBC gRPC to query
    inserts a height field in the gRPC headers that serves as a query hint for the full node to generate proofs against a specific state root
    adds conversion traits between proto and domain types modeling the IBC RPC protocol

* relayer(requests): conversion for `QueryClientState`s

* relayer(requests): conversion for `QueryConsensusState`s

* chain(penumbra): use gRPC IBC service in consensus/client reqs

* chain(penumbra): stuff `height` in grpc headers

* chain(penumbra): override `latest_height` flag in consensus state reqs

* chain(penumbra): prefer gRPC for proof queries

* chain(requests): add conversion trait for `QueryChannelRequest`

* chain(penumbra): rely on gRPC for chan_open handshake

* chain(penumbra): fmt