Generate shared drive usage report CSV

Based of !30 (merged) - so that needs merging first

Was going to update https://gitlab.developers.cam.ac.uk/uis/devops/gsuite/operational-documentation/-/snippets/255 but thought it was about time to add this functionality to the gdrivemanager tool, especially as it already had google drive and lookup api client code.

First two commits is the splitting the manage.py (and its tests) as it was just too big (so reviewing each commit may be easier).

Example output CSV: https://drive.google.com/file/d/1LW0W8UIm9AIAAoLo1ePiFzNZ4BYGor2Q/view?usp=drive_link

Added to Google Sheet: https://docs.google.com/spreadsheets/d/1kqIiOfKoCmLkdS5VHvxUIREKMAVtW-OHd9I_k9qHmjE/edit