srgb feature flag to say 'Individual Gradebook View'

fixes CNVS-12253

test plan:
 - on the course Feature Options settings page
 - the srgb feature flag should now read:
   'Individual Gradebook View'
 - check the description as well
 - that wasn't so bad, right?

Change-Id: I312fbe0a833fb49aa71d35ab5bec74d655574f9d
Reviewed-on: https://gerrit.instructure.com/33021
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>