Feat/support multimodal embedding (#29115)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/services/file_service.py

@@ -1,3 +1,4 @@
+import base64
 import hashlib
 import os
 import uuid
@@ -123,6 +124,15 @@ class FileService:
 
         return file_size <= file_size_limit
 
+    def get_file_base64(self, file_id: str) -> str:
+        upload_file = (
+            self._session_maker(expire_on_commit=False).query(UploadFile).where(UploadFile.id == file_id).first()
+        )
+        if not upload_file:
+            raise NotFound("File not found")
+        blob = storage.load_once(upload_file.key)
+        return base64.b64encode(blob).decode()
+
     def upload_text(self, text: str, text_name: str, user_id: str, tenant_id: str) -> UploadFile:
         if len(text_name) > 200:
             text_name = text_name[:200]