Persist seats in use and owed during cron update

What does this MR do?

UpdateMaxSeatsUsedForGitlabComSubscriptionsWorker was a crontab job triggered daily, for updating max_seats_used. It is now updated to also persist "seats in use" and "seats owed".

Part of customers-gitlab-com#1641 (closed)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.