[FIX] project: Access to attachments with CDN

- The attachments in the tasks page on the portal can be accessed by
  clicking on them.
  They are delivered by the controllers at URL `/web/content/XXXXX`.

  By default when enabling the Content Delivery Network feature on the
  website module, the content delivered by the controller
  `/web/content/` is done through the CDN which has no user account,
  thus may not have access to the attachment.

  To fix the issue, we disable the CDN feature for the attachments in
  the tasks portal page.

  OPW-194571

closes odoo/odoo#31924

Signed-off-by: Toufik Benjaa (tbe) <tbe@odoo.com>