[SM] Create transparency about User Overage process
# Summary
Part of the QSR initiative to bring transparency to user overage process.
Epics for SaaS work:
- https://gitlab.com/groups/gitlab-org/-/epics/7229+
- https://gitlab.com/groups/gitlab-org/-/epics/7230+
### Possible solutions:
1. Add messaging about user overage process to purchase flow
2. Add messaging about user overage process to user invite/management flow
3. Send introductory email about user overages after purchase or renewal (After a GitLab subscription has been purchased or renewed, email the sold to contact to make them aware of how users are counted and how overages are handled)
4. Send a monthly email detailing seat usage and possible overages - https://gitlab.com/groups/gitlab-org/-/epics/6130+
epic