feat(infra): update terraform state backend and add missing runtime secrets

infra/terraform/versions.tf

@@ -1,6 +1,11 @@
 terraform {
   required_version = ">= 1.8.0"
 
+  backend "gcs" {
+    # The bucket will need to be configured via `terraform init -backend-config="bucket=<YOUR_BUCKET>"`
+    # or you can hardcode the bucket name here. Since it's a generic module, we leave it to be configured via init args.
+  }
+
   required_providers {
     google = {
       source  = "hashicorp/google"