Added GCS notification support (#335)

* Added GCS notification support

* fixed notification output indices

* merged vars and added more conditional validation

* Terraform linting

* Added sa_email serviceAccount variable

* Fixed bool check and use try in notification var

* Fixed typo source path example block

* Fixed assert number tftest gcs example

modules/gcs/outputs.tf

@@ -23,7 +23,14 @@ output "name" {
   description = "Bucket name."
   value       = google_storage_bucket.bucket.name
 }
-
+output "notification" {
+  description = "GCS Notification self link."
+  value       = local.notification == true ? google_storage_notification.notification[0].self_link : null
+}
+output "topic" {
+  description = "Topic ID used by GCS."
+  value       = local.notification == true ? google_pubsub_topic.topic[0].id : null
+}
 output "url" {
   description = "Bucket URL."
   value       = google_storage_bucket.bucket.url