async genImageIframeCsr(prompt, messageId) {
    const { contentUrl } = await this.genImagePage(prompt, messageId)
    return this.createImageIframe(contentUrl)
  }
Create a client side render iframe which just points to the image creation page.
Note: If this element is returned to client side, the client must be logged in
to bing.com in order to generate the image successfully. The user's cookie is
required for the polling requests of the generation process.
@param prompt {string} - The prompt for the image generation. It should be given by 'Sydney'.
@param messageId {string} - The message ID refers to the message of 'Sydney'.
@returns {string} The html string of the iframe created.