add Sequence Parallelism

[HaoshengZou]

What does this PR do?

add Sequence Parallelism (#4733 #5024 #5207 #5815 #5841 etc.)
direct plug&play use at https://github.com/Qihoo360/360-LLaMA-Factory

We have a separate README and chat-group at https://github.com/Qihoo360/360-LLaMA-Factory, only for Sequence Parallelism part. They are not to be merged.
We developed based on LLaMA-Factory's latest release v0.9.1. We also based on https://github.com/zhuzilin/ring-flash-attention. The original repos are fully acknowledged.
We developed this at 360. I am PhD from Tsinghua-CS Prof. Jun Zhu's group.

Feel free to review and comment on changes as you see fit. We'll make it better.
Thank you!

Before submitting

• Did you read the contributor guideline?
• Did you write any new necessary tests?

[hiyouga]

Hi Haosheng, thanks a lot for your contribution, we have left some comments, could you kindly revise the code according them?

[LiuLinyun]

我看里面的 seq padding 是直接 pad 到 cutoff_len, 不知道我对这个提交的理解是否有偏差。若样本长度普遍偏短，是否会出现计算浪费？
I see it is padded to cutoff_len, not max len of a micro batch, whether am I misunderstood. If most samples are shoter then cutoff_len, there are a lot of computation waste.