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

api/schedule/clean_unused_datasets_task.py

@@ -1,13 +1,14 @@
-import logging
-import app
 import datetime
+import logging
 import time
+
+import app
 import click
-from flask import current_app
-from werkzeug.exceptions import NotFound
 from core.index.index import IndexBuilder
 from extensions.ext_database import db
-from models.dataset import Dataset, DatasetQuery, Document, DatasetCollectionBinding
+from flask import current_app
+from models.dataset import Dataset, DatasetCollectionBinding, DatasetQuery, Document
+from werkzeug.exceptions import NotFound
 
 
 @app.celery.task(queue='dataset')