docs: def add_entity(self, property_name, use_context=True):
          """
          Add entity property to schema
          :param property_name: str, property name
          :param use_context: bool, whether custom context should be used
          :return: shiftschema.property.EntityProperty
          """
          if self.has_property(property_name):
              err = 'Property "{}" already exists'
              raise PropertyExists(err.format(property_name))
          prop = EntityProperty(use_context=bool(use_context))
          self.entities[property_name] = prop
          return prop