add payment _instrument_id to payment_processor & payment_processor_type tables

There are a few places in the code where use of a payment processor causes payment_type to be set to credit card. I think we want this to be set to the type appropriate to the processor (debit / credit etc) and while I think the payment processor should set the default I think the type should ultimately be site- configurable - hence I think a DB field makes sense. I'm proposing to add the db field at this stage & set the default to credit card at the api level & add an upgrade that sets them all to 1 initially (current behaviour).

I'm not taking responsibility at this stage to getting them correct for ones that aren't credit card or exposing via the ui - but payment processors will at least be able to correctly define i their mgd files