Routine background task that cleans up users that are inactive

Created by: mike-r-mclaughlin

Requested by: https://github.com/sourcegraph/accounts/issues/6716 via Slack thread

Feature request description

It would be nice if there was a background task that could be configured to automatically clean up "inactive" users (defined as users that have not had any activity in more than X days).

Is your feature request related to a problem? If so, please describe.

Customers would like that if users logged in and never came back, they should be removed.

Currently, customers are running a custom cleanup_users.py script (or in the future using src users cleanup.

Describe alternatives you've considered.

Running the above mentioned scripts in a cron job.

/cc @sourcegraph/iam