[security] Hide sensitive informations during account creation

Hi there !

Some people (and I) noticed that when you want to create an account, if your email is invalid, you have a big error with all valid DNS. It is easy to reproduce. Go to the [creation](https://auth.code.gouv.fr/auth/realms/codegouv/login-actions/registration?client_id=sill) page and write anything in the mail.

Could we change this error to write something more general ? Like, "sorry u can't give a wrong email or maybe your administration is not in our list, please contact us :) "

Some thoughts ?