Assign logged only the assignee (user_id), archive/unarchive logged nothing.
Migration 018 adds actor_user_id/actor_service_account_id to incident_events
for 'assigned'; archive/unarchive now log archived/unarchived events with the
caller via callerActorIDs. Timeline JSON gains actor_* fields; web timeline
renders them. Service accounts are still not assignable.
Niklas Ye