[FIX] core: non-stored binary fields should have attachment=False

This prevents some code (in controllers) to retrieve an attachment for a
field that is not stored, as the code only relies on `field.attachment`.
This also makes the field definition more consistent.

closes odoo/odoo#57969

X-original-commit: 13397943d9e953815ae5ce9b01ce812a92903361
Signed-off-by: Raphael Collet (rco) <rco@openerp.com>