add ConsumerGroupConfig Timeout config when use reader

[bloatfan]

i want to increase ConsumerGroup Timeout config when use reader, but no place to config

https://github.com/segmentio/kafka-go/blob/v0.4.48/reader.go#L739

	if r.useConsumerGroup() {
		r.done = make(chan struct{})
		r.runError = make(chan error)
		cg, err := NewConsumerGroup(ConsumerGroupConfig{
			ID:                     r.config.GroupID,
			Brokers:                r.config.Brokers,
			Dialer:                 r.config.Dialer,
			Topics:                 r.getTopics(),
			GroupBalancers:         r.config.GroupBalancers,
			HeartbeatInterval:      r.config.HeartbeatInterval,
			PartitionWatchInterval: r.config.PartitionWatchInterval,
			WatchPartitionChanges:  r.config.WatchPartitionChanges,
			SessionTimeout:         r.config.SessionTimeout,
			RebalanceTimeout:       r.config.RebalanceTimeout,
			JoinGroupBackoff:       r.config.JoinGroupBackoff,
			RetentionTime:          r.config.RetentionTime,
			StartOffset:            r.config.StartOffset,
			Logger:                 r.config.Logger,
			ErrorLogger:            r.config.ErrorLogger,
                         Timeout: // want to config
		})
		if err != nil {
			panic(err)
		}
		go r.run(cg)
	}