How to use the rsocket-core.FLAGS.METADATA function in rsocket-core

_buildSetupFrame(config: ClientConfig): SetupFrame {
    const {keepAlive, lifetime, metadata} = config.setup;

    return {
      flags: FLAGS.METADATA,
      keepAlive,
      lifetime,
      majorVersion: MAJOR_VERSION,
      minorVersion: MINOR_VERSION,
      metadataMimeType: 'application/binary',
      metadata,
      dataMimeType: 'application/binary',
      data: undefined,
      resumeToken: null,
      streamId: CONNECTION_STREAM_ID,
      type: FRAME_TYPES.SETUP,
    };
  }
}