### 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
---------
Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
### What problem does this PR solve?
Refactor Dataset API
### Type of change
- [x] Refactoring
---------
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>
