@Override
                public void onSuccess(ClientResponse resp) {
                    successHandler.handle(fetchTarget, data, resp);
                }
Creates the {@link FetchRequest.Builder fetch request},
{@link NetworkClient#send(ClientRequest, long) enqueues/sends it, and adds the {@link RequestFuture callback}
for the response.

@param fetchRequests  {@link Map} of {@link Node nodes} to their
                      {@link FetchSessionHandler.FetchRequestData request data}
@param successHandler {@link ResponseHandler Handler for successful responses}
@param errorHandler   {@link ResponseHandler Handler for failure responses}
@return List of {@link RequestFuture callbacks}
clients/src/main/java/org/apache/kafka/clients/consumer/internals/Fetcher.java