Banea Dominios

Creating logic for banning specific email domains.
Since here we're validating the domains that could be banned by admins, and we're not validating the user emails, after talking about it with @Fernan2 we think that we could get rid "dominio_con_caracteres_invalidos" and "dominio_es_un_sufijo" validations.

The user email validation will look for an exact match with a banned domain introduced by admin. So that will make our work easier.