add the current user to sis imports

fixes: CNVS-11546

Adds a user relation to sis batches so we can relate a sis batch job back to the
user who initiated it.

Test Plan:
  - Initiate SIS Imports.
  - The associated sis batch records user_id column should have the correct value.

  * SIS Imports should not be broken.

Change-Id: Ic5d0807af4d945a150a0268776e51c6db96b29c6
Reviewed-on: https://gerrit.instructure.com/31172
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Nick Cloward <ncloward@instructure.com>