Update prime-server-ingress.yaml
Update prime-server-ingress.yaml

updated deprecated api version and updated spec syntax.

https://cloud.google.com/kubernetes-engine/docs/release-notes#deprecated_apis
https://v1-19.docs.kubernetes.io/docs/reference/generated/kubernetes-api/v1.19/#ingressbackend-v1-networking-k8s-io
https://stackoverflow.com/questions/64125048/get-error-unknown-field-servicename-in-io-k8s-api-networking-v1-ingressbacken
GoogleCloudPlatform/gke-migration-to-containers,GoogleCloudPlatform/gke-migration-to-containers