feat: support reading tags via API (#12891) (#13732)

### What problem does this PR solve?

Enable reading Tag Set tags via API (expose tag_kwd field). The result
of the queried list chunks is as shown below:

<img width="1422" height="818" alt="image"
src="https://github.com/user-attachments/assets/abd1960a-fe34-489e-9d72-525f8e574938"
/>


### Type of change

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

Co-authored-by: heyang.why <heyang.why@alibaba-inc.com>

sdk/python/ragflow_sdk/modules/chunk.py

@@ -28,6 +28,7 @@ class Chunk(Base):
         self.id = ""
         self.content = ""
         self.important_keywords = []
+        self.tag_kwd = []
         self.questions = []
         self.create_time = ""
         self.create_timestamp = 0.0