Add support for the Gutenberg module

Problem/Motivation

This module does not work on content types that are set up to use Gutenberg → .
This issue is a feature request so we can use Real-time SEO for Drupal inside the Gutenberg editor.

I read that this does not work correctly here and I can confirm this.

Steps to reproduce

- Install yoast_seo and gutenberg module
- create a content type with a body field and a Real-time SEO field
- Enable the Gutenberg experience for the content type
- Create a node with content in the Gutenberg editor

The Real-time SEO does not work. For any given keyword the status is 'Bad', I am quite sure the code does not actually check the Gutenberg page content.

Proposed resolution

Make this module work in combination with the Gutenberg module