https://github.com/infiniflow/ragflow/issues/3651
### What problem does this PR solve?
_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### 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)
---------
Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
### What problem does this PR solve?
feat: support AWS Bedrock #308
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
