feat: integrate VikingDB Knowledge Base into rag retrieving tool (#381)

Co-authored-by: Henry Li <henry1943@163.com>

src/rag/__init__.py

@@ -3,6 +3,15 @@
 
 from .retriever import Retriever, Document, Resource, Chunk
 from .ragflow import RAGFlowProvider
+from .vikingdb_knowledge_base import VikingDBKnowledgeBaseProvider
 from .builder import build_retriever
 
-__all__ = [Retriever, Document, Resource, RAGFlowProvider, Chunk, build_retriever]
+__all__ = [
+    Retriever,
+    Document,
+    Resource,
+    RAGFlowProvider,
+    VikingDBKnowledgeBaseProvider,
+    Chunk,
+    build_retriever,
+]