[IMP] mail: add first lightweight support of qweb in rendering mixin

PURPOSE

Make digest email and tips more appealing. The goals of these tips are

  * to encourage the adoption of other apps (Did you know ?);
  * to make Odoo look more fun (Fun tips and tricks, young and dynamic style);
  * to show social proof and increase trust (emphasis on already existing
    projects / customers to);

SPECIFICATIONS

In this commit we simply add a first support of tools to render qweb templates
like rendering jinja. Instead of giving the template to render the xml id of
the view is passed.

This code is meant to be improved in a near future with new use cases that
will soon arise.

LINKS

Task ID 2197417
PR odoo/odoo#51619