Enable CORS for k8s

[gothub]

Enable CORS in the Kubernetes ingress that will be serving bookkeeper request.

https://stackoverflow.com/questions/25775364/enabling-cors-in-dropwizard-not-working#25801822

See NCEAS/metadig-engine#255

[gothub]

The CORS headers will be enabled by updating the associated NGINX virtual server manifest that will be either in the metadig-engine repo (where the current NGINX definitions are) or in a new repo that contains all NGINX manifests, that are now common to metadig-engine and bookkeeper. I'll update this issue when those changes are made.