datafix missing observer enrollments from sis imported enrollments

fixes #CNVS-16391

Change-Id: I37943039912d88e2ea3946fa5c2fcacbf9909265
Reviewed-on: https://gerrit.instructure.com/44416
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>