[FIX] link_tracker: add a system parameter to disabled the tracking

Bug
===
If you send a URL (which will be transformed into a link tracker) to
an external website (e.g. in mass mailing, social, ...), the UTM values
will be added in the GET parameters of the URL.

The external website might crash if those parameters are not supported
by it.

We want to add a system parameter `link_tracker.no_external_tracking`
to be able to not add those UTM values in the redirected URL.

This is done only for external website, because it will never be an
issue if the URL redirect to Odoo.

Task-2657413

closes odoo/odoo#77493

Signed-off-by: awa-odoo <awa-odoo@users.noreply.github.com>