'require_usage_rights' feature flag

test plan:
 - as site admin, set feature to 'allowed' in a root account
 - as a teacher in a course under this account, see that feature
   becomes available to be allowed in course settings

closes CNVS-15864

Change-Id: I569e6febf44bcf75a46bcbbbc25d15a99571cc46
Reviewed-on: https://gerrit.instructure.com/44567
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>

lib/feature.rb

@@ -295,6 +295,14 @@ END
       applies_to: 'Course',
       state: 'allowed',
       development: true
+    },
+    'usage_rights_required' =>
+    {
+      display_name: -> { I18n.t('Require usage rights for uploaded files') },
+      description: -> { I18n.t('If enabled, content designers must provide copyright and license information for files before they are published') },
+      applies_to: 'Course',
+      state: 'hidden',
+      root_opt_in: true
     }
   )