Accessing Alibaba Cloud OSS with Amazon S3 SDK

### What problem does this PR solve?

Add license statement.

### Type of change

- [x] Refactoring

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

https://github.com/infiniflow/ragflow/issues/2503


### 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] New Feature (non-breaking change which adds functionality)

Before:

<img width="611" alt="image"
src="https://github.com/user-attachments/assets/02a3a1ee-7bfb-4fe0-9b15-11ced69cc8a3">

After:

<img width="796" alt="image"
src="https://github.com/user-attachments/assets/371136af-8d16-47aa-909b-26609d3ad60e">

<img width="557" alt="image"
src="https://github.com/user-attachments/assets/9268362f-2b6a-4ea1-9fe7-659f7292e5e1">

### What problem does this PR solve?

issue: https://github.com/infiniflow/ragflow/issues/2277

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [ ] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>