### What problem does this PR solve?
Add api for sessions and add max_tokens for tenant_llm
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
### What problem does this PR solve?
#1853
### Type of change
- [X] New Feature (non-breaking change which adds functionality)
Co-authored-by: Zhedong Cen <cenzhedong2@126.com>