Additional file formats for file upload and fine control on types allowed

## Current state

In the first implementation we decided to accept these file formats:
- PDF
- Word (doc, docx)
- Excel (xls, xlsx)
- CSV
- PNG
- JPG
- TXT

## Consider exploring adding additional missing requested file formats:

- JSON
- XML
- PowerPoint (PPT / PPTX)
- Email (MSG)
- MP4
- ZIP
- KML
- etc.

Considerations around https://github.com/cds-snc/platform-forms-client/issues/6300

## AND More fine control on file upload types (at the extension level)

## Source

**Feature request from support ticket:**
https://cds-snc.freshdesk.com/a/tickets/26156
http://cds-snc.freshdesk.com/a/tickets/29504

> - Other file upload types (.json, .xml, .zip)
> - More fine control on file upload types (at the extension level)

Start by locating the existing file-upload implementation and reviewing related issue #6300; the payload does not name a file or test. Clarify the supported formats and extension-level controls, then verify that uploads accept the agreed formats and reject unsupported extensions.

Written by the indexing model from the issue text.