Support passing transaction fees to practitioner when purchasing privileges

[landonshumway-ia]

The ASLP and OT compacts want practitioners to pay for the transaction fees charged by the Compact's Merchant Service Provider (Authorize.net's MSP charges 2.9% + 30 cents per transaction). We need to support getting this transaction fee rate to the frontend so it can display it to the user, and the backend needs to add this as a line item when processing transactions in Authorize.net.

This ticket involves updating the backend to support this feature through our compact configuration, as well as our privilege purchasing endpoint to start storing these extra fees.

[landonshumway-ia]

Capturing notes from standup for future reference:

• Currently, NONE of the compacts will be splitting transaction fees across jurisdictions
• The COUN compact will cover these fees themselves, as mentioned above the ASLP and OT compacts will pass these fees onto the practitioner
• We need to account for the fact that by adding the transaction fee as a line item to the transaction, the total also increases and this in turn makes the ACTUAL transaction percentage fee larger (we need to determine how to handle rounding in this scenario)
• We will likely handle this by adding two new fields to the compact configuration files, one to define what the compact's actual transaction fee rate is, and another to define if this fee is to be passed onto the practitioner.

[isabeleliassen]

• need to calculate total so frontend can pull from backend and avoid discrepancy

[landonshumway-ia]

Capturing information from meeting with EDs for future reference:

• We will be using a fixed flat rate for the transaction fee, which will be set in the compact configuration, and charged once per privilege
• The flat rate will be shown in a separate line item with the title 'Credit Card Transaction Fee'