record enrollment time on task

fixes ALYT-29

test plan:
  * access pages in a course for at least two minutes
  * open the course people page
  * verify that Total Activity reflects your time spent

Change-Id: I3b7765ae9469a9ce1d4258b7edfc161cf196f17b
Reviewed-on: https://gerrit.instructure.com/35377
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>
QA-Review: August Thornton <august@instructure.com>