Support knowledge metadata filter (#15982)

api/core/rag/index_processor/constant/built_in_field.py

@@ -0,0 +1,15 @@
+from enum import Enum
+
+
+class BuiltInField(str, Enum):
+    document_name = "document_name"
+    uploader = "uploader"
+    upload_date = "upload_date"
+    last_update_date = "last_update_date"
+    source = "source"
+
+
+class MetadataDataSource(Enum):
+    upload_file = "file_upload"
+    website_crawl = "website"
+    notion_import = "notion"