code: def update_metadata(self, scaling_group, metadata):
          
          if not isinstance(scaling_group, ScalingGroup):
              scaling_group = self.get(scaling_group)
          curr_meta = scaling_group.metadata
          curr_meta.update(metadata)
          return self.update(scaling_group, metadata=curr_meta)
docs: Adds the given metadata dict to the existing metadata for the scaling
          group.