Add endpoint for serving i18n requests
    
    For now JSON service is not available without authentication
    to IPA. But some of Web UI pages expect translations before
    or without Login process. This endpoint serves i18n requests
    only.
    
    Fixes: https://pagure.io/freeipa/issue/7559
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>