Feat/dify rag (#2528)

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

api/core/rag/models/document.py

@@ -0,0 +1,16 @@
+from typing import Optional
+
+from pydantic import BaseModel, Field
+
+
+class Document(BaseModel):
+    """Class for storing a piece of text and associated metadata."""
+
+    page_content: str
+
+    """Arbitrary metadata about the page content (e.g., source, relationships to other
+        documents, etc.).
+    """
+    metadata: Optional[dict] = Field(default_factory=dict)
+
+