Authorize.net Settings

Alters the commerce_authnet settings form to allow overriding a few settings
used to communicate with Authorize.net. After enabling, you'll see some new
fields at the bottom of the Authorize.net AIM payment method settings.

Strictly speaking, this module is unnecessary. The settings can already be
set via Drupal variables using Drush. However, it is sometimes convenient to
be able to set them via the admin ui.

It seemed like there was bound to already be a module that did this, but I
didn't find it.

IMPORTANT NOTE: adjusting the SSL/TLS version requires the patch at:
https://www.drupal.org/project/commerce_authnet/issues/2929488

It'll look like you can set it if you just install the module, but if you
don't also patch commerce_authnet, your changes won't do anything.