There is a need to check if public key in the RPC response matches the
public key of the related storage node declared in network map.
Define `ErrWrongPublicKey` error. Implement RPC response handler's
constructor `AssertKeyResponseCallback` which checks public key. Construct
handler and pass it to client's option `WithResponseInfoHandler`.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
