Adjusting otp_form.html to work on Wagtail 6

[helmantel]

The fields block in otp_form.html now needs to make use of the formattedfield template tag since the field template tag can no longer be used in Wagtail 6:

{% block fields %}
    {% formattedfield field=form.otp_token %}
    {% block extra_fields %}
        {% for field_name, field in form.extra_fields %}
            {% formattedfield field=field %}
        {% endfor %}
    {% endblock extra_fields %}
{% endblock %}