TCHAP: add warning modal if email on authentification is external #415

When user mistype their email, they will be redirected to the external server, which should not be the case

If we detect it is an external email, we prompt this modal, otherwise it is directly redirected to the MAS

Clicking on continue: redirect to the MAS
Clicking on cancel: stay on the email verification page

Si on peut garder le même texte :)