Purchase API endpoint makes 'test' purchase with authorize.net Sandbox account (ASLP compact only)

[landonshumway-ia]

As a licensee, I need to be able to purchase privileges in different jurisdictions. The API endpoint will support this by using authorize.net to make purchases. As part of our first slice of this feature, we will use a authorize.net Sandbox account, which will allow us to test the purchase functionality without actually making real payments.

A new endpoint will be added to our api POST /purchases/privileges (schema TBD) which will be callable for a licensee in the ASLP
compact in a testing environment.

Design created and implemented for securely storing authorize.net credentials in Secrets Manager and fetching them. (This would best be supported with an API endpoint through which an Admin would upload the authorize.net credentials ie POST /purchases/configuration/upload)