Forms subjects : simplify / refactor / re-arrange whole documentation

[thomasnares]

Form subjects in the documentation are discussed at several locations:

• /development/components/form
• /development/components/form/types-reference/
• /development/architecture/migration-guide/forms/
• /modules/creation/adding-configuration-page-modern/
• /development/architecture/migration-guide/forms/settings-forms/

We have also several example modules to show how to interact with forms.

Cross linking has been done (https://github.com/PrestaShop/docs/pull/1762) but improvements can be done :

• the page : /development/components/form has duplicated content with some of the others
• it may be difficult for a module developer to understand the differences between those documentations, example modules, ...

We should think about a new structure around forms & PrestaShop, maybe with 2 approaches:

• Forms & PrestaShop for core developers
• Forms & PrestaShop for module developers