Use terraform to config GCP proxy setup

With terraform (https://terraform.io) we can convert most of the infrastructure setup into code. This simplifies setting up a new proxy as well as providing reproducibility in the setup, eliminating human errors as much as possible.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190634711

java/google/registry/proxy/terraform/modules/gke/output.tf

@@ -0,0 +1,3 @@
+output "proxy_instance_group" {
+  value = "${google_container_cluster.proxy_cluster.instance_group_urls[0]}"
+}