Use Sylius templates events for displays

[maximehuran]

It could be nice for admin and shop to use sylius template events to do the displays without rewrite the templates.

• Ui Event for admin channel form
• Ui event for shop checkout complete form
• Ui event for shop address form

Example for admin channel form

        sylius.admin.channel.form.second_column_content:
            blocks:
                mailchimp:
                    template: '/Admin/Channel/Form/_mailchimp.html.twig'
                    priority: 9

And in the template

<div class="ui attached segment">
    {{ form_row(form.displaySubscribeToNewsletterAtCheckout) }}
</div>