Changes to Create a klarna gateway

added the new optional request property data/attributes/idempotency_window_mins

added the optional property data/attributes/idempotency_window_mins to the response with the 201 status

added the new required request property data/relationships/klarna_payments/data

request property data/type was restricted to a list of enum values

removed the request property data/relationships/klarna_payments/id

removed the request property data/relationships/klarna_payments/type

added the new optional request property data/attributes/_disable

added the new optional request property data/attributes/_enable

added the new optional request property data/attributes/force_payments

the type request property default value klarna_gateways was removed

added the new klarna_gateways enum value to the request property data/type

added the media type application/vnd.api+json for the response with the status 201