Change Carpool Charter URL in email notifications

In all email notifications, the Carpool Charter is included in the footer.

Currently the URL is an old one redirecting to a Notion page.

Expected: Redirect user to this URL when clicking on "See the Carpool Charter":

• EN email notifications: https://caroster.io/en/carpool-charter
• FR email notifications: https://caroster.io/charte-de-covoiturage