fix: open mfe modal editor of new duplicated xblock (#36641)

When duplicating an xblock in the authoring MFE, the iframe was opening its own editor modal instead of the MFE modal.

cms/djangoapps/contentstore/rest_api/v1/serializers/course_waffle_flags.py

@@ -29,6 +29,7 @@ class CourseWaffleFlagsSerializer(serializers.Serializer):
     use_new_group_configurations_page = serializers.SerializerMethodField()
     enable_course_optimizer = serializers.SerializerMethodField()
     use_react_markdown_editor = serializers.SerializerMethodField()
+    use_video_gallery_flow = serializers.SerializerMethodField()
 
     def get_course_key(self):
         """
@@ -160,3 +161,9 @@ class CourseWaffleFlagsSerializer(serializers.Serializer):
         """
         course_key = self.get_course_key()
         return toggles.use_react_markdown_editor(course_key)
+
+    def get_use_video_gallery_flow(self, obj):
+        """
+        Method to get the use_video_gallery_flow waffle flag
+        """
+        return toggles.use_video_gallery_flow()

cms/djangoapps/contentstore/rest_api/v1/views/course_waffle_flags.py

@@ -61,8 +61,9 @@ class CourseWaffleFlagsView(APIView):
             "use_new_course_team_page": true,
             "use_new_certificates_page": true,
             "use_new_textbooks_page": true,
-            "use_new_group_configurations_page": true
+            "use_new_group_configurations_page": true,
             "use_react_markdown_editor": true,
+            "use_video_gallery_flow": true
         }
         ```
         """

cms/djangoapps/contentstore/rest_api/v1/views/tests/test_course_waffle_flags.py

@@ -34,6 +34,7 @@ class CourseWaffleFlagsViewTest(CourseTestCase):
         'use_new_updates_page': True,
         'use_new_video_uploads_page': False,
         'use_react_markdown_editor': False,
+        'use_video_gallery_flow': False,
     }
 
     def setUp(self):