Allow to download attachment from custom widget link when ACL are applied

[maluhialoha]

Describe the problem to be solved

Should be solved by #1614, but documenting it here so we can test :)

It is not currently possible to download an attachment from a custom widget, if acl are applied on the table containing the attachment.

Steps to reproduce:

• create a table with an "attachment" column, and a custom widget with an attachment download link built with grist.docApi.getAccessToken()
• Add an "email" column to the table and add a row with the email of another account, and an attachment in the "attachment" column
• Add acl to the table user.Email == rec.Email --> everything allowed
• Make the document public (or share the document as editor to your other account)
• In another browser, log in with this account and open the document
• Place your cursor on the row you're allowed to see, open the link displayed in the custom widget and see that you can't download the attachment:
  error 403 Forbidden
  "Cannot access attachment"
• Remove the acl from the document, and see that the download is ok

ex file: https://public.getgrist.com/hnxjBVBRKJ1Z/Attachments-in-builder

Describe the solution you would like

Being able to download attachments even if there are acl on the table.

Linked to #1512 (comment)