[FIX] website: better helper for domain in settings

If the user type his website URL as suggested by the helper, and he redirects
his `http` to `https` (nginx, cloudflare..), then his canonical url won't ever
be reachable.
Most critical issue will be that we won't display the `alternate/hreflang` tag,
which basically tells the search engines what and where is our translated
content.

opw-2486918

closes odoo/odoo#69056

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