code: public ClientFactoryBuilder workerGroup(EventLoopGroup workerGroup, boolean shutdownOnClose) {
          this.workerGroup = requireNonNull(workerGroup, "workerGroup");
          shutdownWorkerGroupOnClose = shutdownOnClose;
          return this;
      }
docs: Sets the worker {@link EventLoopGroup} which is responsible for performing socket I/O and running
  {@link Client#execute(ClientRequestContext, Request)}.
  If not set, {@linkplain CommonPools#workerGroup() the common worker group} is used.
  
  @param shutdownOnClose whether to shut down the worker {@link EventLoopGroup}
  when the {@link ClientFactory} is closed