Implement `Client.Conn` method which returns underlying connection as
`io.Closer`. Method is going to be used for forwarding the connection to
superior clients.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Implement gRPC client that can uniformly execute any RPC on the remote
server. In the primary implementation, the client is a thin wrapper over
gRPC client connection that is required to create the client. In the future,
it is planned to expand the library with convenient functionality.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
