Return a fully-qualified session_entity_type string.

def session_entity_type_path(cls, project, session, entity_type):
        """Return a fully-qualified session_entity_type string."""
        return google.api_core.path_template.expand(
            'projects/{project}/agent/sessions/{session}/entityTypes/{entity_type}',
            project=project,
            session=session,
            entity_type=entity_type,
        )