Wagtail Forms - Upload Image Field - Add enctype to Form Page View

form_page.html

{% extends "base.html" %}
{% load wagtailcore_tags %}

{% block content %}
    {{ self.intro }}
    <form action="{% pageurl self %}" method="POST" enctype="multipart/form-data">
        {% csrf_token %}
        {{ form.as_p }}
        <input type="submit">
    </form>
{% endblock %}