make additional sort options visible in prod ui
make additional sort options visible in prod ui

closes TALLY-469
flag=new_gradebook_sort_options

Test Plan:
1. Make sure the 'Additional Sort Options for New Gradebook' feature
   flag is visible and toggleable in your local canvas setup.

Change-Id: I30a2fbe8f5c450643a45a7d022e46d194acad63f
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/223793
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Product-Review: Spencer Olson <7cc0890d6f1f70810a023e7173eca5724d6c8e49@instructure.com>
Reviewed-by: Keith Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>
Reviewed-by: Adrian Packel <9c6a39807293376f29cba17542b4cb1b663ecc4a@instructure.com>
QA-Review: Robin Kuss <0b206b54367b2de0334896ea45826f0e3194bd35@instructure.com>

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