Feature Request: Add functionality to the guestbook to require documents (such as signed agreements, etc.) to be uploaded

Overview of the Feature Request
In a guestbook, provide functionality to require that a user must upload one or more (usually signed by the user) specific documents.

For ADA, this would be handy for Access Requests where the user needs to submit signed agreements, or deeds, etc.
Document upload for Guestbook-at-Download wouldn't be used by ADA very much if at all, but perhaps there are others who would find that handy.

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

For both the end user requesting data, and for the admin-type user evaluating requests.

What inspired the request?

For ADA and certain datasets, requesters must submit signed agreements, etc.

This has always been done to date by the user emailing it in separately which requires a maintenance overhead in not only associating the forms with a given request/ticket but finding them at a later date when that user requests other data requiring the same submitted form. It would be handier to be able to submit the form/s as part of the guestbook response so that the documents are kept with the request. Reduces the number of emails for the requester and approver, and makes it clear to the requester what is required for a complete access request.

Any brand new behavior do you want to add to Dataverse?

Add document upload as part of guestbook response.
Indicate which documents are required, and make them "required" or "optional" (to cover that use case) as needed.

Any open or closed issues related to this feature request?
I can't find any in an initial cursory search (apologies if there is one already).

Are you thinking about creating a pull request for this feature?
ADA does not have the resources for contributing to this feature request.

The request names no files, tests, or entry points. Start by locating guestbook response handling and the related request storage and user/admin interfaces; done should include configurable required or optional document uploads retained with the corresponding request.