add differentiated modules flag

closes LF-607
flag=differentiated_modules
qa risk: none

test plan:
-specs pass

Change-Id: I6afbeee70b570dd9aeecce919b33c13e729e659c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/325380
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jackson Howe <jackson.howe@instructure.com>
QA-Review: Jake Oeding <jake.oeding@instructure.com>
Product-Review: Jake Oeding <jake.oeding@instructure.com>

app/controllers/application_controller.rb

@@ -360,6 +360,7 @@ class ApplicationController < ActionController::Base
     permanent_page_links
     developer_key_page_checkboxes
     improved_no_results_messaging
+    differentiated_modules
   ].freeze
   JS_ENV_ROOT_ACCOUNT_FEATURES = %i[
     product_tours

config/feature_flags/learning_foundations_release_flags.yml

@@ -233,3 +233,11 @@ improved_no_results_messaging:
     If enabled, the course link tray will display more helpful messaging
     if there are no results for a given resource type.
   applies_to: SiteAdmin
+
+differentiated_modules:
+  state: hidden
+  display_name: Differentiated Modules
+  description: |-
+    If enabled, modules and module items become assignable to specific
+    individuals and groups.
+  applies_to: SiteAdmin

ui/shared/global/env/EnvCommon.d.ts

@@ -175,6 +175,7 @@ export type SiteAdminFeatureId =
   | 'permanent_page_links'
   | 'developer_key_page_checkboxes'
   | 'improved_no_results_messaging'
+  | 'differentiated_modules'
 
 /**
  * From ApplicationController#JS_ENV_ROOT_ACCOUNT_FEATURES