UserMerge: move scheduler appointments

fixes CNVS-9716

test plan:
  1. As a teacher, using the scheduler, create a set of appointment groups.
  2. As an admin, create two user accounts, and enroll them into the course
    with the appointment groups.
  3. Sign into each user account and using the scheduler, sign up for
    different scheduled appointment times.
  4. As an admin, merge these two accounts.
  5. As the user, navigate to the Scheduler and observe that the scheduled
    appointment tied to the current account is still tied to the account. but
    the other that is tied to the old account has not updated to reflect being
    tied to the new account.

Change-Id: I69b4b0fd46774d6096b48189132190183ac4eb4a
Reviewed-on: https://gerrit.instructure.com/29640
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>