MerchantTransactionId for Payouts

We have added merchantTransactionId to the request and response of the POST /payouts endpoint. This is your unique
identifier for the API request that can be used when a connection issue occurs, and you don't receive a paymentId. We
will validate the uniqueness of the merchantTransactionId value per retail channel. If a payment/payout/refund is
created with merchantTransactionId abc, no other payment/payout/refund can be created with abc. If this happens we
will return an HTTP Status 409 Conflict with a 4701 response code.

The merchantTransactionId is a contract between BR-DGE and a merchant. This field will not be mapped downstream to any
PSP.

We have also added a new GET payouts endpoint to our API which requires a merchantTransactionId as a query parameter,
this endpoint will return a payout in a list structure. If no payout can be found relating to this
merchantTransactionId, we will return an HTTP Status 200 and an empty list.