Feat/dify rag (#2528)

Co-authored-by: jyong <jyong@dify.ai>

api/core/rag/datasource/vdb/field.py

@@ -0,0 +1,10 @@
+from enum import Enum
+
+
+class Field(Enum):
+    CONTENT_KEY = "page_content"
+    METADATA_KEY = "metadata"
+    GROUP_KEY = "group_id"
+    VECTOR = "vector"
+    TEXT_KEY = "text"
+    PRIMARY_KEY = " id"