Support for Yoast Focus Keyword, meta description and seo title

[jphorn]

This is a follow-up request from an older Github issue which has since been closed: #86

The issue was closed because you (then) chose to piggyback onto Yoast's own checks for Readability Analysis and SEO Analysis score. However, I don't think that's the correct approach as the green (or orange) bullets are a) easy to game and b) not a very good indicator and c) it's even discouraged by team Yoast.

Especially their number 1 item rings true: "1. Not every post or page has to be optimized". We have many different custom post types, and they don't all need optimisation. BUT they might sometimes need a focus keyword or a filled-in SEO meta description. Right now I can't make this a hard requirement in Checklists Pro, and that prevents me from a global rollout on our site.

We always used Requirement Checklists (Classic Editor only, and now seemingly abandoned) and they had these checks. Also I noticed HumanMade/Altis Publication Checklist offer a similar check for SEO Title (ref).

I would really love to see these separate Yoast SEO checks in Checklists (Pro) instead of (imho incorrectly) relying on the SEO assessment analysis.

Thank you for considering.