Re-export tonic in cln-grpc

[ErikDeSmedt]

Using cln-grpc in an outside crate is somewhat tricky. We currently do not have a way to describe the type of T in NodeClient<T>

The export allows the user to write the snippet below.

struct App {
  grpc_client: NodeClient<cln_grpc::tonic::transport::Channel>
}

impl App {

  fn create(destination: AsRef<str>) -> Self {
    NodeClient::connect(destination.as_ref())
      .await
      .unwrap("Failed to connect")
  }
}

async fn main() {
  App::create("http://localhost:1234")
}