feature:Add OceanBase Storage Support for Table Parser (#12923)

### What problem does this PR solve?

close #12770 

This PR adds OceanBase as a storage backend for the Table Parser. It
enables dynamic table schema storage via JSON and implements OceanBase
SQL execution for text-to-SQL retrieval.


### 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):

### Changes
- Table Parser stores row data into `chunk_data` when doc engine is
OceanBase. (table.py)
- OceanBase table schema adds `chunk_data` JSON column and migrates if
needed.
- Implemented OceanBase `sql()` to execute text-to-SQL results.
(ob_conn.py)
- Add `DOC_ENGINE_OCEANBASE` flag for engine detection (setting.py)

### Test
1. Set `DOC_ENGINE=oceanbase` (e.g. in `docker/.env`)
<img width="1290" height="783" alt="doc_engine_ob"
src="https://github.com/user-attachments/assets/7d1c609f-7bf2-4b2e-b4cc-4243e72ad4f1"
/>

2. Upload an Excel file to Knowledge Base.(for test, we use as below)
<img width="786" height="930" alt="excel"
src="https://github.com/user-attachments/assets/bedf82f2-cd00-426b-8f4d-6978a151231a"
/>

3. Choose **Table** as parsing method.
<img width="2550" height="1134" alt="parse_excel"
src="https://github.com/user-attachments/assets/aba11769-02be-4905-97e1-e24485e24cd0"
/>

4.Ask a natural language query in chat.
<img width="2550" height="1134" alt="query"
src="https://github.com/user-attachments/assets/26a910a6-e503-4ac7-b66a-f5754bbb0e91"
/>

rag/app/table.py

@@ -457,10 +457,10 @@ def chunk(filename, binary=None, from_page=0, to_page=10000000000, lang="Chinese
                 txts.extend([str(c) for c in cln if c])
         clmns_map = [(py_clmns[i].lower() + fields_map[clmn_tys[i]], str(clmns[i]).replace("_", " ")) for i in
                      range(len(clmns))]
-        # For Infinity: Use original column names as keys since they're stored in chunk_data JSON
+        # For Infinity/OceanBase: Use original column names as keys since they're stored in chunk_data JSON
         # For ES/OS: Use full field names with type suffixes (e.g., url_kwd, body_tks)
-        if settings.DOC_ENGINE_INFINITY:
-            # For Infinity: key = original column name, value = display name
+        if settings.DOC_ENGINE_INFINITY or settings.DOC_ENGINE_OCEANBASE:
+            # For Infinity/OceanBase: key = original column name, value = display name
             field_map = {py_clmns[i].lower(): str(clmns[i]).replace("_", " ") for i in range(len(clmns))}
         else:
             # For ES/OS: key = typed field name, value = display name
@@ -480,9 +480,9 @@ def chunk(filename, binary=None, from_page=0, to_page=10000000000, lang="Chinese
                     continue
                 if not isinstance(row[clmns[j]], pd.Series) and pd.isna(row[clmns[j]]):
                     continue
-                # For Infinity: Store in chunk_data JSON column
+                # For Infinity/OceanBase: Store in chunk_data JSON column
                 # For Elasticsearch/OpenSearch: Store as individual fields with type suffixes
-                if settings.DOC_ENGINE_INFINITY:
+                if settings.DOC_ENGINE_INFINITY or settings.DOC_ENGINE_OCEANBASE:
                     data_json[str(clmns[j])] = row[clmns[j]]
                 else:
                     fld = clmns_map[j][0]
@@ -490,8 +490,8 @@ def chunk(filename, binary=None, from_page=0, to_page=10000000000, lang="Chinese
                 row_fields.append((clmns[j], row[clmns[j]]))
             if not row_fields:
                 continue
-            # Add the data JSON field to the document (for Infinity only)
-            if settings.DOC_ENGINE_INFINITY:
+            # Add the data JSON field to the document (for Infinity/OceanBase)
+            if settings.DOC_ENGINE_INFINITY or settings.DOC_ENGINE_OCEANBASE:
                 d["chunk_data"] = data_json
             # Format as a structured text for better LLM comprehension
             # Format each field as "- Field Name: Value" on separate lines