Added capability to ignore fields -in register form- when creating them

[mariajgrimaldi]

This PR avoids raising errors when:

1. A field is added to REGISTRATION_EXTRA_FIELDS
2. We aren't interested in creating its definition dictionary because we don't want to render the field. For that, we don't want to raise any errors to not cause noise in sentry.

This is done to cover a special case with authorized_email field.

Now, to ignore it we will have to add the setting EDNX_IGNORE_REGISTER_FIELDS : ["authorized_email"]