Add audit event for impersonated events

Overview

We added the start and end of impersonation in #315 (closed), but we should annotate any user event that is being performed while a user's being impersonated.

Proposal

In audit events, an impersonated event should be attributed to the user account but note that the action was done while being impersonated by an admin.

• Record the admin who impersonated the user in each event, in addition to the impersonated user, when an admin takes an action while impersonating a user.

A simple solution may be:

Impersonation: User took some action in project. (by: administrator)