Differentiate "debug" from "logging"

Other WooCommerce extensions (like for Shipping and Payment) have debug options that show verbose output to admins in several places, including (but not limited to): Order Notes and Checkout.

Adding this functionality will help merchants more quickly diagnose problems and/or confirm that WCS is working as expected.


See https://github.com/Automattic/woocommerce-services/issues/223 for more detail.

EDIT:

- [ ] Catalogue what types of debug messages/data are shown by existing shipping and payment extensions
- [ ] Determine what useful debugging information can be shown by our plugin without (and with) server changes
- [ ] Write up a proposal for the changes to be made

Start by reviewing issue #223 and the debug options in existing shipping and payment extensions. Catalogue the debug messages shown in places such as Order Notes and Checkout, then identify what useful information WooCommerce Services can expose without or with server changes. Done means a written proposal covering the requested debugging behavior and scope.

Written by the indexing model from the issue text.