Move GCP proxy code to the old [] proxy's location

1. Moved code for the GCP proxy to where the [] proxy code used to live.
3. Corrected reference to the GCP proxy location.
4. Misc changes to make ErrorProne and various tools happy.

+diekmann to LGTM terraform whitelist change.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=213630560

java/google/registry/proxy/terraform/example_config.tf

@@ -0,0 +1,31 @@
+terraform {
+  backend "gcs" {
+    # The name of the GCS bucket that stores the terraform.tfstate file.
+    bucket = "YOUR_GCS_BUCKET"
+    prefix = "terraform/state"
+  }
+}
+
+module "proxy" {
+  source                   = "../../modules"
+  proxy_project_name       = "YOUR_PROXY_PROJECT"
+  gcr_project_name         = "YOUR_GCR_PROJECT"
+  proxy_domain_name        = "YOUR_PROXY_DOMAIN"
+  proxy_certificate_bucket = "YOU_CERTIFICATE_BUCKET"
+}
+
+output "proxy_service_account" {
+  value = "${module.proxy.proxy_service_account}"
+}
+
+output "proxy_name_servers" {
+  value = "${module.proxy.proxy_name_servers}"
+}
+
+output "proxy_instance_groups" {
+  value = "${module.proxy.proxy_instance_groups}"
+}
+
+output "proxy_ip_addresses" {
+  value = "${module.proxy.proxy_ip_addresses}"
+}