Add prefix to project factory SA bindings

Co-authored-by: Antonio Lopez <ajln@google.com>

examples/factories/project-factory/main.tf

@@ -24,10 +24,11 @@ locals {
   }
   _group_iam_bindings = distinct(flatten(values(var.group_iam)))
   # internal structures for project service accounts IAM bindings
+  _project_id = coalesce(var.prefix, "") == "" ? var.project_id : "${var.prefix}-${var.project_id}"
   _service_accounts_iam = {
     for r in local._service_accounts_iam_bindings : r => [
       for k, v in var.service_accounts :
-      "serviceAccount:${k}@${var.project_id}.iam.gserviceaccount.com"
+      "serviceAccount:${k}@${local._project_id}.iam.gserviceaccount.com"
       if try(index(v, r), null) != null
     ]
   }