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.

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

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

@@ -0,0 +1,13 @@
+variable "proxy_service_account_email" {}
+
+variable "proxy_cluster_region" {}
+
+variable "proxy_cluster_zones" {
+  type = "map"
+
+  default = {
+    americas = "us-east4-a"
+    emea     = "europe-west4-b"
+    apac     = "asia-northeast1-c"
+  }
+}