提供多天流式训练的demo

[welsonzhang]

System information

• DeepRec version (you are using):
• Are you willing to contribute it (Yes/No):yes

Describe the feature and the current behavior/state.
推荐一般需要回溯很多天的数据，进行eval/train 流式训练，可以提供多天流式训练的demo例子吗? 例如这种：
https://github.com/PaddlePaddle/PaddleRec/blob/master/doc/online_trainer.md

Will this change the current api? How?

Who will benefit with this feature?

Any Other info.