Feature Request: Allow for single checkbox option in custom guestbook question

Overview of the Feature Request
Users have started to use the guestbook feature as a method of asking files downloaders to "Agree" to a dataset's stated Terms of Use. This seems similar to how one "agrees" to the Terms of Use for any other software application.

Currently, the guestbook supports this in some way by allowing a collection admin to create a custom question. This is an example:

It would be great to be able to have a single checkbox option that downloaders can check to indicate agreement rather than typing "I agree" in a single line entry.

The guestbook allows collection admins to create a custom "multiple choice" question, however this option requires two or more answers. I would like to create the option to include only one possible response. This would allow for the creation of a question such as: "I agree to the dataset's stated Terms of Use" with a single response option: "I agree."

What kind of user is the feature intended for?
(Example users roles: API User, Curator, Depositor, Guest, Superuser, Sysadmin)
Dataverse collection admin

What inspired the request?
Users building workflows to use the guestbook as an additional mechanism to alert file downloaders to the dataset's Terms of Use.

What existing behavior do you want changed?
Allow the "multiple choice" custom question type in a guestbook to support single answers.

Any brand new behavior do you want to add to Dataverse?
No.

Any open or closed issues related to this feature request?
No

Are you thinking about creating a pull request for this feature?
No.

Start by tracing the guestbook custom-question flow used by collection admins, focusing on multiple-choice questions and the validation that currently requires two or more answers. Check how the guestbook form stores and displays question options, then identify the relevant tests. Done means a multiple-choice guestbook question can contain one response option, such as “I agree,” and downloaders can submit it.