add reset content event

fixes: CNVS-12590

Adds a course content event type to the course audit logs.

Test Case:

  - Create a course.
  - Reset its content.
  - The event and its data should be reflected for both
    the source course and new course from resetting the
    course data.

Change-Id: I473d2e237491d890c20aace57f9c7675d70d22c7
Reviewed-on: https://gerrit.instructure.com/33726
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Nick Cloward <ncloward@instructure.com>