Returns:

• formFields: fields currently on the form (id, name, label, mandatory flag, error message, order)
• listFields: list fields that can be placed on the form (id, name, label)

The list must belong to the authenticated account and the form must belong to the given list.

Note: formFields does not include each field's options (for radio/horizontalradio/
select/textmulti fields). If you intend to re-submit this list to update_form, see the
warning on that endpoint's fields property before doing so.