An idempotent (paid) B request gives different `payment` values in the response

[lukehesluke]

For a paid activity, if a 2nd (idempotent) B request is made, it includes different fields in .payment than the 1st response

This screenshot shows an example JSON diff:

The left hand side is the response from the 1st B request and the right hand side is the response from the 2nd B request. identifier is different in each and some fields are added/removed.

Tests that fail:

• non-free-opportunities_opportunity-paid-idempotency_OpenBookingSimpleFlow_IndividualFacilityUseSlot.html.zip

[nathansalter]

The additional properties and identifier should be returned in the first B response

[nathansalter]

We should return the additional properties for Metadata in the C2 response

[nickevansuk]

Broker note: additionalProperty on Payment will be available at B, and must be included within the metadata of the Stripe PaymentIntent before capture, so that payments can be correctly routed by the Booking System.

[nickevansuk]

When we retest this, need to ensure that additionalProperty on PaymentIntent is the same and included at both "B" and "idempotent B"