Modify gke/grpc-bookstore.yaml to use GKE ingress for container native load balancing.

[shuoyang2016]

Modify gke/grpc-bookstore.yaml to use GKE ingress for container native load balancing.

These sample code is being used by https://cloud.google.com/endpoints/docs/grpc/get-started-kubernetes-engine-espv2. Changes in this PR include:

• TLS secret is attached to both ingress and ESPv2.
• Service type is changed from "LoadBalancer" to "ClusterIP" because ingress will start manage the external load balancer.

There are also a few Google internal docs changes pending:

• Users will create an IP alias enabled cluster in creating a container cluster section.
• Users will configure TLS because container native LB uses HTTP2 and TLS is a must to have.

[shuoyang2016]

@nareddyt @qiwzhang @TAOXUY PTAL.

[shuoyang2016]

Makes sense. I just changed it to 443.

[shuoyang2016]

Thank you @nareddyt @TAOXUY . I'll try to submit this together with the internal doc change diff.