Reformat imports with isort (#3123)

Besides that:
1. Introduce `setup.py isort` for quick check
2. Introduce GH actions to check imports

tests/test_log.py

@@ -2,11 +2,13 @@ import logging
 import os
 import sys
 import unittest
-import yaml
+
 from io import StringIO
-from queue import Queue, Full
+from queue import Full, Queue
 from unittest.mock import Mock, patch
 
+import yaml
+
 from patroni.config import Config
 from patroni.log import PatroniLogger