Support for Plaid Transfer

[shaunek-hero]

We've found this project very helpful for dealing with Plaid Link/Auth, kudos to the authors! This is a request to add support for the Plaid Transfer product, which is for creating and managing bank transactions such as ACH, RTP, and FedNow transactions within the US.

Product Overview: https://plaid.com/docs/transfer/
API detail: https://plaid.com/docs/api/products/transfer/

I see that this library has support for the Plaid Bank Transfers product, which seems to be very similar to Plaid Transfer - perhaps Bank Transfers is a previous iteration of Transfer? I don't really know the history, just that Plaid Transfer is the publicly advertised product that isn't in beta. My team is rolling out a new project with Plaid Link + Plaid Transfer and it would have been nice to use this library for both Plaid products instead of just Plaid Link.