Improve transport to write in batches to increase throughput

[ronenhamias]

currently transport sends messages and write and flush on each request

private void send(Channel channel, Message message, CompletableFuture<Void> promise) {
    if (promise == COMPLETED_PROMISE) {
      channel.writeAndFlush(message, channel.voidPromise());
    } else {
      composeFutures(channel.writeAndFlush(message), promise);
    }
  }

write and flush create a syscall on each message reducing throughput an alternative approach might be by write in batches so flush will be done periodical on favor with the right balance between latency and throughput.