[META] Integrate seo assessments [#2906977]

Problem/Motivation

As an editor I want to get SEO assessments on the node form.

Proposed resolution

Use YoastSeo.js for integrating a seo analysis and search snippet preview on the node form. The analysis will be generated against a focus keyword field and the node preview, triggered by an additional submit button the results will be displayed in a modal. Configuration should be handled in widget settings.

We decided against using the yoast_seo module for their approach using individual fields as content input, which does not seem viable for paragraphs / inline entity forms.

Assessment should be generated based on
* Meta title
* Meta description
* Url path
* Full content based on preview
* Keyword field (persisting)

Results display (provided by YoastSeo.js)
* Snippet Preview (without snippet editor)
* Various content and seo assessments