Gateway: Grant myself the role roles/monitoring.admin

Another attempt to work around hashicorp/terraform-provider-google#2605

environments/_modules/gateway/stackdriver.tf

@@ -1,6 +1,6 @@
 resource "google_project_iam_binding" "stackdriver_dashboard_editor" {
   // Grant ourselves permission to create workspaces because Terraform doesn't support it:
   // https://github.com/hashicorp/terraform-provider-google/issues/2605
-  role = "roles/monitoring.dashboardEditor"
+  role = "roles/monitoring.admin"
   members = [var.sre_iam_uri]
 }