move rescue_responses to app config

fixes CNVS-14289

Change-Id: Icadcbee1c31436322fb53a4b5263c30f3381c3a3
Reviewed-on: https://gerrit.instructure.com/38016
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>