include user id in submission sidebar cache key
include user id in submission sidebar cache key

in case the user id changes after a merge

closes #CORE-810

Change-Id: Ie3b383a78a9ea1397a837522d849b464b8d603b7
Reviewed-on: https://gerrit.instructure.com/136620
Tested-by: Jenkins
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Product-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
QA-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms