docs: def list_indexes(cls):
          """
          Returns a dictionary with the key as the es_index name and the
          object is a list of rdfclasses for that index
  
          args:
              None
          """
  
          cls_list = cls.list_mapped_classes()
          rtn_obj = {}
          for key, value in cls_list.items():
              idx = value.es_defs.get('kds_esIndex')[0]
              try:
                  rtn_obj[idx].append(value)
              except KeyError:
                  rtn_obj[idx] = [value]
          return rtn_obj