add integration_data, integration_id for assignment through api

Test Plan: see SIS-281

fixes SIS-281

Change-Id: I25b7d18a7cd752826ff38d0f795cba0059b56df1
Reviewed-on: https://gerrit.instructure.com/35071
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Eric Adams <eadams@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>