docs: def save(self, *args, **kwargs):
          """
          call synchronizer "after_external_layer_saved" method
          for any additional operation that must be executed after save
          """
          after_save = kwargs.pop('after_save', True)
          super(LayerExternal, self).save(*args, **kwargs)
          # call after_external_layer_saved method of synchronizer
          if after_save:
              try:
                  synchronizer = self.synchronizer
              except ImproperlyConfigured:
                  pass
              else:
                  if synchronizer:
                      synchronizer.after_external_layer_saved(self.config)
          # reload schema
          self._reload_schema()