setGreetingText(text) {
    const greeting = (typeof text !== 'string') ? text : [{
      locale: 'default',
      text
    }];
    return this.sendProfileRequest({ greeting });
  }
Set a greeting text for new conversations. The Greeting Text is only rendered the first time the user interacts with a the Page on Messenger.
Facebook docs: https://developers.facebook.com/docs/messenger-platform/reference/messenger-profile-api/greeting
@param {String|Array.<Object>} text Greeting text, or an array of objects to support multiple locales. For more info on the format of these objects, see: https://developers.facebook.com/docs/messenger-platform/reference/messenger-profile-api/greeting