Vista Checkout configuration help text link goes to a non-existent page

Problem/Motivation

The help link for how to configure Visa Checkout is broken. The current link leads to a 404 page on Authorize.net.

https://developer.authorize.net/api/reference/features/visa_checkout.html#Enrolling_in_Visa_Checkout

How to reproduce

1. go to /admin/commerce/config/payment-gateways
2. click "add payment gateway"
3. select the following plugin option: Authorize.net (Visa Checkout)
4. The help text under the "Visa Checkout API Key" field has a link for instructions on where to get the API key. That link goes to a non-existent page

Resolution

Track down the appropriate documentation page and update the link to Authorize.net's configuration documentation.