Archiving a group should create an audit event

Ensure that when a group is archived via the UI or API, an audit event is created.

Implementation plan

Take inspiration from project archival Add audit events for API archive calls via serv... (!197348 - merged) and update Groups::ArchiveService and Groups::UnarchiveService.

References

• https://docs.gitlab.com/user/compliance/audit_events/#group-audit-events
• https://docs.gitlab.com/api/audit_events/#group-audit-events
• https://docs.gitlab.com/development/audit_event_guide/