[IMP] base, http_routing, website: allow custom routing rule

After this commit, you will be able (in technical mode) to update the url for
the python controllers.

Eg.
You can now rename /shop in /garden and /shop/product/ in /garden/vegetable/

Most of urls will be replaced at fly in the renderd qweb, with the function
url_for but all old urls will keep available. So if you access url /shop you
will be automatically redirected to /garden (308 Permanent Redirect).

As for cdn and other post-process of att, the automatically replacement in the
rendered qweb is only done when you will be not website editor. But the new
dispatch of URL will be applied in all cases.

For developper, since it is Permanent Redirect, don't forget to clear cache or
open chrome debug tool (with option 'Disable cache while DevTools is Open) to
see your lasts changes.

closes odoo/odoo#36555

Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>