### What problem does this PR solve?
feat: Implement file upload and folder creation features
- Add file upload route in router.go
- Add file operation methods in dao/file.go
- Add util/file.go for file type detection and filename handling
- Implement file upload and folder creation endpoints in handler/file.go
- Implement file upload and folder creation logic in service/file.go
- Modify response message format in memory.go
- Add document count method in dao/document.go
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
Feat： Add Memory function by go
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
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Co-authored-by: Yingfeng <yingfeng.zhang@gmail.com>
