Create user report fetch/check

Story

As a compliance officer, I would like to include a user role report in my auditree checks, So that I can have a report of all accounts with access to cloud.gov

Solution

### Tasks
- [x] Refine https://github.com/GSA/notifications-api/blob/main/terraform/ops/cloudgov_user_report.py as the fetcher
- [x] Figure out if a specific check is useful, beyond the empty/abandoned checks