Add isort to the pre-commit configuration and apply it to the whole project (#595)

* Apply isort to the entire repository
* Fix missing import issues in text_to_entries
* Fix imports in migration files

tests/test_plaintext_to_entries.py

@@ -1,12 +1,9 @@
-# Standard Packages
 import json
 import os
 from pathlib import Path
 
 from khoj.database.models import KhojUser, LocalPlaintextConfig
 from khoj.processor.content.plaintext.plaintext_to_entries import PlaintextToEntries
-
-# Internal Packages
 from khoj.utils.fs_syncer import get_plaintext_files
 from khoj.utils.rawconfig import TextContentConfig