improve: introduce isort for linting Python imports (#1983)

api/core/index/base.py

@@ -1,9 +1,9 @@
 from __future__ import annotations
-from abc import abstractmethod, ABC
-from typing import List, Any
 
-from langchain.schema import Document, BaseRetriever
+from abc import ABC, abstractmethod
+from typing import Any, List
 
+from langchain.schema import BaseRetriever, Document
 from models.dataset import Dataset