unhide new gradebook feature flag for all accounts
unhide new gradebook feature flag for all accounts

This switches the default behaviour of the New Gradebook feature flag
from hidden to allowed so all non-site-admin can allow the New
Gradebook

fixes GRADE-635

test plan:
 - As a non-site-admin is the New Gradebook feature flag visible to
 be set to allowed
 - One the non-site-admin sets it to allow, as a teacher, can you see
 the feature flag on a course

Change-Id: I796cba83bffe9a9a6eb48f0495f4ac96a85e31c8
Reviewed-on: https://gerrit.instructure.com/131527
Tested-by: Jenkins
Reviewed-by: Derek Bender <d24d8a7ee520e34b1cec38800225d9f36b552df7@instructure.com>
Reviewed-by: Jeremy Neander <20252aad5efdc666f083d82ab63ed0f9f72a043e@instructure.com>
QA-Review: KC Naegle <9fbecd016338f9910821a8a5d5d0ae4fc9abfaa5@instructure.com>
Product-Review: Matt Goodwin <7c47e89894930304a2cdfa1d2ccca1e1eddb893d@instructure.com>

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