ConsumeTimestamp选项无法设置，导致ConsumeFromTimestamp没有意义

[happylhb]

consumer.WithConsumeFromWhere(consumer.ConsumeFromTimestamp) 但无法设置ConsumeTimestamp
通过代码来看，也没有计算最近半小时的选择

//consumer/consumer.go  line:784

case ConsumeFromTimestamp:
	if lastOffset == -1 {
		if strings.HasPrefix(mq.Topic, internal.RetryGroupTopicPrefix) {
			lastOffset, err := dc.queryMaxOffset(mq)
			if err == nil {
				result = lastOffset
			} else {
				result = -1
				rlog.Warning("query max offset error", map[string]interface{}{
					rlog.LogKeyMessageQueue:  mq,
					rlog.LogKeyUnderlayError: err,
				})
			}
		} else {
			t, err := time.Parse("20060102150405", dc.option.ConsumeTimestamp)
			if err != nil {
				result = -1
			} else {
				lastOffset, err := dc.searchOffsetByTimestamp(mq, t.Unix()*1000)
				if err != nil {
					result = -1
				} else {
					result = lastOffset
				}
			}
		}
	}
default:

[maixiaohai]

try this #681
you can set consumer offset by timestamp through console