Feedback endpoint support

[mseckykoebel]

Actions being accepted, declined, or ignored by a CDS client are important metrics that services can use to improve. CDS hooks 1.1 implements feedback, or a way to POST feedback to a CDS service with information on how an action was taken on the client.

Implementing feedback in Sero would allow a client to POST (POST {baseUrl}/cds-services/{serviceId}/feedback) feedback for every service on a server made with Sero.