### What problem does this PR solve?

Refactor API for document and session.

### Type of change


- [x] Refactoring

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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

Refactor Chat API

### Type of change

- [x] Refactoring

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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

Refactor Dataset API

### Type of change

- [x] Refactoring

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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

1. dataset: create/delete/list/get/update
2. files in dataset: upload/download/list/delete/get_info

### Type of change

- [x] Documentation Update

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Signed-off-by: Jin Hai <haijin.chn@gmail.com>