Submit button helper for confirmation forms

[simonrjones]

We have a need for a confirmation form that contains:

• Hidden CSRF token
• Cancel link
• Submit button to confirm action
• Confirm action text (e.g. Yes, please delete this user)
• Cancel text (e.g. Cancel and go back)
• We may want to add hidden fields
• Must be a POST request

Example HTML for confirmation form:

<form action="/admin/users/2685638/delete" method="post">
        <input type="hidden" name="_token" value="rBJaVcSi6dzbMuInRi6SvnFgKr0kgiSAAq978Iex" autocomplete="off">
        <p>
            <a href="https://www.rnibbookshare.org/admin/users/2685638" class="rnib-button rnib-button--secondary">
                Cancel and go back
            </a>

            <button type="submit" class="rnib-button rnib-button--primary">
                Yes, please delete this user
                <svg viewBox="0 0 8 16" class="icon icon--chevron rnib-button__icon" aria-hidden="true" focusable="false">
                    <path d="M3.692 0H0l4.308 8L0 16h3.692L8 8 3.692 0Z" fill="currentColor"></path>
                </svg>
            </button>
        </p>
    </form>