Refactoring metaboxes and CPT creation

[Kenshino]

Issue Description

The current CPT creation uses a custom plugin that won’t see regular maintenance. It’s better to use a maintained plugin such as CMB2 and extended-CPTs etc.

Context

Phase 2 of Helphub will require greater capabilities that the current CPT plugin offers. It’ll make sense for us to fix the fundamentals before we move in deeper.

[carl-alberto]

Anyone assigned on this one @Kenshino? Would love to help on this part.

[Kenshino]

No one, feel free to start on a feature branch @carl-alberto