D401 Support - Root and Misc Files

[ferruzzi]

Part of #10742

D401 asserts "First line should be in imperative mood". This is a little opaque so upon further investigation what they want is:

[Docstring] prescribes the function or method's effect as a command: 
("Do this", "Return that"), not as a description; 
e.g. don't write "Returns the pathname ...".

We started with over two thousand violations in the repo so I'm going to take this in bites.

PLEASE NOTE

There should be zero logic changes in this PR, only changes to docstrings and whitespace. If you see otherwise, please call it out.

Included in this chunk

All files located in the following modules:

• airflow/main.py
• airflow/configuration.py
• airflow/policies.py
• airflow/sentry.py
• helm_tests/other/test_keda.py
• setup.py

To test

If you uncomment this line and run pre-commit in main you will get over a thousand errors. After these changes, no files in the list above should be on the list. After re-commenting that line and re-running pre-commits, there should be zero regressions.