SDK is missing Processor response codes

[tzubertowski]

General information

• SDK/Library version: latest stable
• Environment: either, it's a feature missing
• Language, language version, and OS: PHP, 8.2.12, Linux

Issue description

Braintree SDK does not provide an extensive list of processor response codes. Thus during integration we need to keep our own enum/constant list of response codes to handle them.

This is not ideal, as it means that whenever a response code is added our constant list becomes incomplete. By providing it in the SDK it would become a programmatic source of truth and not require us to webscrap Braintree's documentation :)