add logger info for newly created slugs

arkindex_worker/worker/element.py

@@ -42,6 +42,7 @@ class ElementMixin(object):
                     "corpus": corpus.id,
                 },
             )
+            logger.info(f"Created a new element type with slug {element_type.slug}")
 
     def check_required_types(
         self, corpus_id: str, *type_slugs: str, create_missing: bool = False