Records inheriting from portal mixin implement their own access to portal
using tokens. Activating the access button by default seems the right thing
to do instead of having to do it manually in each addon. Access is granted
at record level using tokens and access URLs anyway.
This eases future improvements of "Pay Now" notification template as it
will use the ``has_access_button`` instead of doing custom computation
directly in the template itself.
Task-2712450 (Mail/Sale: Improve 'Pay Now' notification template)
Part-of: odoo/odoo#82627