[FIX] mass_mailing: don't short url before rendering

Before this commit, if you generate the href with jinja/mako syntax,
the un-rendered url will be shortened.

So:
    href="https://www.odoo.com?id=${object.id}"
will become:
    href="https://www.odoo.com/r/asw"

where
   https://www.odoo.com/r/asw
redirect to
   https://www.odoo.com?id=${object.id}
instead of
   https://www.odoo.com?id=1

Adaptation of #28540 for 11.0 version.

opw-1903803
closes #29083