Automate clean-up of users that are no longer using Codecov #163

[rohan-at-sentry]

Problem
Customers run out of seats, and sometimes it's because of users who aren't accessing codecov (users who no longer work at the org, test user accounts set up during eval etc)

Solution
Clean 'em up

Notes

This is from a customer, although I'd like to post this more generally to see if others in the community have faced similar issues