Register new email.

def register_email(request):
    '''
    Register new email.
    '''
    user = request.user

    serializer = RegisterEmailSerializer(data=request.data)
    serializer.is_valid(raise_exception=True)

    email = serializer.validated_data['email']

    template_config = (
        registration_settings.REGISTER_EMAIL_VERIFICATION_EMAIL_TEMPLATES)
    if registration_settings.REGISTER_EMAIL_VERIFICATION_ENABLED:
        signer = RegisterEmailSigner({
            'user_id': user.pk,
            'email': email,
        }, request=request)
        send_verification_notification(
            user, signer, template_config, email=email)
    else:
        email_field = get_user_setting('EMAIL_FIELD')
        setattr(user, email_field, email)
        user.save()

    return get_ok_response('Register email link email sent')