[FIX] website_slides: prevent slide download for public users
[FIX] website_slides: prevent slide download for public users

Task #1930691

Purpose
=======

If the download security is set to 'Authenticated users', the route should prevent public users
from downloading the slides.

closes #30281

closes odoo/odoo#30399
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo