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/iam.tf

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+resource "google_service_account" "proxy_service_account" {
+  account_id = "proxy-service-account"
+  display_name = "Nomulus proxy service account"
+}
+
+resource "google_project_iam_member" "nomulus_project_viewer" {
+  project = "${var.nomulus_project_name}"
+  role = "roles/viewer"
+  member = "serviceAccount:${google_service_account.proxy_service_account.email}"
+}
+
+resource "google_project_iam_member" "gcr_storage_viewer" {
+  project = "${var.gcr_project_name}"
+  role = "roles/storage.objectViewer"
+  member = "serviceAccount:${google_service_account.proxy_service_account.email}"
+}
+
+resource "google_project_iam_member" "metric_writer" {
+  role = "roles/monitoring.metricWriter"
+  member = "serviceAccount:${google_service_account.proxy_service_account.email}"
+}
+
+resource "google_project_iam_member" "log_writer" {
+  role = "roles/logging.logWriter"
+  member = "serviceAccount:${google_service_account.proxy_service_account.email}"
+}