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/kms.tf

@@ -0,0 +1,16 @@
+resource "google_kms_key_ring" "proxy_key_ring" {
+  name = "${var.proxy_key_ring}"
+  location = "global"
+}
+
+resource "google_kms_crypto_key" "proxy_key" {
+  name = "${var.proxy_key}"
+  key_ring = "${google_kms_key_ring.proxy_key_ring.id}"
+}
+
+resource "google_kms_crypto_key_iam_member" "ssl_key_decrypter" {
+  crypto_key_id = "${google_kms_crypto_key.proxy_key.id}"
+  role = "roles/cloudkms.cryptoKeyDecrypter"
+  member = "serviceAccount:${google_service_account.proxy_service_account.email}"
+}
+