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

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

src/rag/builder.py

@@ -3,12 +3,15 @@
 
 from src.config.tools import SELECTED_RAG_PROVIDER, RAGProvider
 from src.rag.ragflow import RAGFlowProvider
+from src.rag.vikingdb_knowledge_base import VikingDBKnowledgeBaseProvider
 from src.rag.retriever import Retriever
 
 
 def build_retriever() -> Retriever | None:
     if SELECTED_RAG_PROVIDER == RAGProvider.RAGFLOW.value:
         return RAGFlowProvider()
+    elif SELECTED_RAG_PROVIDER == RAGProvider.VIKINGDB_KNOWLEDGE_BASE.value:
+        return VikingDBKnowledgeBaseProvider()
     elif SELECTED_RAG_PROVIDER:
         raise ValueError(f"Unsupported RAG provider: {SELECTED_RAG_PROVIDER}")
     return None