Metadata: add endpoint to the group

def metadata_add_endpoints(self):
        """ Metadata: add endpoint to the group """
        metadata = load_mpe_service_metadata(self.args.metadata_file)
        group_name = metadata.get_group_name_nonetrick(self.args.group_name)
        for endpoint in self.args.endpoints:
            metadata.add_endpoint(group_name, endpoint)
        metadata.save_pretty(self.args.metadata_file)