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.

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

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

@@ -0,0 +1,32 @@
+module "proxy_gke_americas" {
+  source = "./gke"
+  proxy_cluster_region = "americas"
+  proxy_service_account_email = "${google_service_account.proxy_service_account.email}"
+  proxy_ports = "${var.proxy_ports}"
+}
+
+module "proxy_gke_emea" {
+  source = "./gke"
+  proxy_cluster_region = "emea"
+  proxy_service_account_email = "${google_service_account.proxy_service_account.email}"
+  proxy_ports = "${var.proxy_ports}"
+}
+
+module "proxy_gke_apac" {
+  source = "./gke"
+  proxy_cluster_region = "apac"
+  proxy_service_account_email = "${google_service_account.proxy_service_account.email}"
+  proxy_ports = "${var.proxy_ports}"
+}
+
+locals {
+  "proxy_instance_groups" = {
+    americas = "${module.proxy_gke_americas.proxy_instance_group}",
+    emea = "${module.proxy_gke_emea.proxy_instance_group}",
+    apac = "${module.proxy_gke_apac.proxy_instance_group}",
+  }
+}
+
+output "proxy_instance_groups" {
+  value = "${local.proxy_instance_groups}"
+}