New payment state REJECTED_PENDING_RETRY

[judgej]

This state is not yet documented, and is not (at time of writing) fully implemented in the API.

It is an intermediate state for a payment between being rejected by SIP and accepted for FPS. As such, it is not an end-state.

The end states for payments are final - the payment record is never changed. We we are given a non-end state, then the payment state will change, keeping the same paymentUid. This is something to consider when storing payments in the database.

[judgej]

No changes to be made until the additions are formally/officially documented.