Free text form element

Is your feature request related to a problem? Please describe.
We discovered an editor was attempting to add content to a review form that wasn't a question (e.g. some contextual text at the beginning and end of the form) by creating a new text field. I expect they thought they could do this because Google Forms has this option.

In this instance, the Editor had also left this hack-y field 'required' and so when the reviewer attempted to input their review, they overlooked the non-question fields and lost their review (resulting in #3766 )

Describe the solution you'd like

Add another option to 'kind' in the Review Form builder that lets an Editor insert text instead of a question, kinda like Google Forms does:

Describe alternatives you've considered
Discouraging editors from attempting to use question fields to convey non-question information.

Additional context
This functionality could also be useful for dividing a Review Form up into sections, each with its own heading and description.

Start by locating the Review Form builder and the code that handles the existing field “kind” options. Trace how fields are created and rendered for editors and reviewers, then define the text option and section headings or descriptions described in the issue. Done means editors can insert non-question text without a required response and reviewers can submit forms without treating it as a question.