Everything that can go to an invoice needs an accountingRef

[ralfbayer-db]

Every part of a booking which can exist on the invoice from an OSDM provider to an OSDM consumer needs to have an accountingRef structure, so that the accounting departments can match items on invoices with items in the bookings.

Currently, only the bookedOfferParts (including booked Fees) have this structure.

However, it is missing from the refundFee and from the exchangeFee.

Other items are ok:

• an OnHoldOffer contains a Fee structure (instead of just a Price), which in turn contains the accountingRef
• CancelFulfillment and Release don't have a fee/price, so they cannot exist on an invoice

Proposal:

• as a non-breaking change, add an accountingRef attribute (of type AccountingRef) to both ExchangeOffers and RefundOffers
• as a breaking change in the next major release, replace the Price structure with a Fee structure for the exchangeFee and refundFee attributes in ExchangeOffer and RefundOffer, respectively

Also, document the understanding that the accountingRef only needs to be filled on confirmed items.

[ralfbayer-db]

Documentation on accounting is also outdatet, it is currently present in these files:

• https://osdm.io/spec/common-data-structures/
• https://osdm.io/spec/business-capabilities/

However, the new accountingRef structure is not mentioned there.

See #570