Provider preselection and remitter accounts for recurring payments

Change to our API for recurring payments
We have deployed a feature to let clients preselect a provider and (optionally) a specific remitter account when creating a new mandate. We are removing the mandate.provider_filter field from the POST /mandates endpoint and replacing it with mandate.provider_selection.

The shape of this object will mirror the one we already have in the POST /payments endpoint (specifically, payment_method.provider_selection). Note that this is a breaking change because the new provider_selection field will be required when creating a new mandate.

To make successful requests, replace the previous usage of provider_filter with provider_selection: { type: "user_selected", filter: <your previous provider_filter, if any> }.

We've updated our documentation and our API to reflect this change.