Impersonation start/stop audit events not appearing on the group-level page

Problem to solve

Audit Events for "impersonation start/stop" are not appearing in the group-level Audit Events page. Although the impersonation actions are appearing, it would be helpful to show the start/stop as well.

Proposal

Audit Events for beginning and ending an impersonation session should appear in the group-level audit log when the impersonated user belongs to a group (in addition to the instance-level audit log as they do already).

In this table, that is represented by the top three rows.

Proposal note

This is about showing instance-level AuditEvents in the group-level Audit log, which is closely related to showing project-level AuditEvents in the group-level Audit log.

Implementation plan

backend weight 3️⃣

1. Update ImpersonationAuditEventService to accept an optional entity.
2. Create a service to create an ImpersonationEvent for each user.groups in batches as a background job.
   • See inserting into tables in batches docs.
   • Do this only for a the user's direct memberships, ie exclude inherited subgroups.
3. Create a Started Impersonation in users_controller.rb using the new service.
4. Create a Stopped Impersonation in application_controller.rb using the new service.
5. Update audit events docs.
6. Update specs.