[IMP] rating: Add a retrocompatibily route

Purpose
=======

Even if the routes are correctly updated and the existing data is
correctly updated, the emails that were already sent to the customers
will be problematic, as we will provide a value which is not handled
anymore (10 for example).

To provide a retrocompatibility, deprecated the old route and
introduce a new one.

closes odoo/odoo#46296

Taskid: 2083096
Related: odoo/upgrade#889
Related: odoo/enterprise#10312
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>