Put maintenance mode behind feature flags

ee/app/controllers/ee/admin/application_settings_controller.rb

@@ -78,7 +78,7 @@ module EE
           attrs << :group_owners_can_manage_default_branch_protection
         end
 
-        if License.feature_available?(:geo)
+        if ::License.feature_available?(:geo) && ::Feature.enabled?(:maintenance_mode)
           attrs << :maintenance_mode
           attrs << :maintenance_mode_message
         end

ee/lib/ee/api/entities/application_setting.rb

@@ -20,8 +20,8 @@ module EE
           expose :updating_name_disabled_for_users, if: ->(_instance, _opts) { ::License.feature_available?(:disable_name_update_for_users) }
           expose :npm_package_requests_forwarding, if: ->(_instance, _opts) { ::License.feature_available?(:packages) }
           expose :group_owners_can_manage_default_branch_protection, if: ->(_instance, _opts) { ::License.feature_available?(:default_branch_protection_restriction_in_groups) }
-          expose :maintenance_mode, if: ->(_instance, _opts) { ::License.feature_available?(:geo) }
-          expose :maintenance_mode_message, if: ->(_instance, _opts) { ::License.feature_available?(:geo) }
+          expose :maintenance_mode, if: ->(_instance, _opts) { ::License.feature_available?(:geo) && ::Feature.enabled?(:maintenance_mode) }
+          expose :maintenance_mode_message, if: ->(_instance, _opts) { ::License.feature_available?(:geo) && ::Feature.enabled?(:maintenance_mode) }
         end
       end
     end

ee/lib/ee/api/settings.rb

@@ -47,7 +47,7 @@ module EE
               attrs = attrs.except(:group_owners_can_manage_default_branch_protection)
             end
 
-            unless License.feature_available?(:geo)
+            unless ::License.feature_available?(:geo) && ::Feature.enabled?(:maintenance_mode)
               attrs = attrs.except(:maintenance_mode, :maintenance_mode_message)
             end
 

ee/spec/controllers/admin/application_settings_controller_spec.rb

@@ -126,6 +126,10 @@ RSpec.describe Admin::ApplicationSettingsController do
     end
 
     context 'updating maintenance mode setting' do
+      before do
+        stub_feature_flags(maintenance_mode: true)
+      end
+
       let(:settings) do
         {
           maintenance_mode: true,

ee/spec/requests/api/settings_spec.rb

@@ -192,6 +192,10 @@ RSpec.describe API::Settings, 'EE Settings' do
   end
 
   context 'maintenance mode' do
+    before do
+      stub_feature_flags(maintenance_mode: true)
+    end
+
     let(:settings) do
       {
         maintenance_mode: true,