Feature Request: Allow document upload as part of access request

Overview of the Feature Request

Allow document upload with an access request.

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

Applicant - to provide documents required (ex. a signed deed) for an access request
Approver - to be able to keep all related items (gb response + documents) together in a single request.

What inspired the request?

ADA has several datasets that require additional documents such as a signed deed to be submitted for an access request.
Applicants have always had to email ADA separately with these documents, then they have to be attached/linked to the access request ticket. It all requires a lot of overhead and manual management.

If those deeds and documents could be submitted as part of the access request, it would keep everything together and require far less tracking and management.

Users often get the signing wrong so being able to send back the request (#11431) with the document and ask them to resubmit with a correct deed would also reduce the manual tracking and management currently required.

What existing behavior do you want changed?

None

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

Allow document upload as part of a request. This would be particularly useful for "Guestbook at Access Request" use case but maybe for "Guestbook at File Download" as well.

Any open or closed issues related to this feature request?

Not sure.

Are you thinking about creating a pull request for this feature?
Help is always welcome, is this feature something you or your organization plan to implement?

ADA does not have the resources to submit code.

No files, tests, or entry points are named in the issue. First map the existing access-request workflow and attachment or linking handling, then define whether uploads apply to guestbook access requests, file downloads, or both; done means applicants can submit documents and approvers can review them within the request, including resubmission.