[Feature request] Add "latest" or "first" option for field's index page

[J-Bot87]

Hi,

In my database containing the file, I don't know the number of file's pages.
I create a template with "/templates/pdf" and I would specifying "latest" in the ["fields"]["areas"]["page"] key.
This way, the field would be placed on the last page of the PDF.

Thanks !

"fields": [ { "name": "purchaser", "type": "signature", "required": true, "uuid": "", "submitter_uuid": "", "areas": [ { "page": "latest", # <-- latest "attachment_uuid": "", "x": 0.7465069860279441, "y": 0.7747993119266054, "w": 0.2, "h": 0.07071277346506705 } ] }