Fix CPT permastruct

[charl0tee]

• rewrite directly when registering CPT => https://github.com/superhuit-agency/pulse-up/blob/client-staging/wordpress/theme/lib/post-types/FeatureType.php#L82-L85
• Test if still need global $post_types for Custom Taxonomy permastruct.
• Update documentation accordingly

[charl0tee]

Linked to #82