Plaid Get incremental transaction updates on a processor token

This endpoint replaces `/processor/transactions/get` and its associated webhooks for most common use-cases. The `/processor/transactions/sync` endpoint allows developers to subscribe to all transactions associated with a processor token and get updates synchronously in a stream-like manner, using a cursor to track which updates have already been seen. `/processor/transactions/sync` provides the same functionality as `/processor/transactions/get` and can be used instead of `/processor/transac...