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/variables.tf

@@ -91,6 +91,18 @@ variable "name" {
   type        = string
 }
 
+variable "notification_config" {
+  description = "GCS Notification configuration."
+  type = object({
+    enabled           = bool
+    payload_format    = string
+    topic_name        = string
+    sa_email          = string
+    event_types       = list(string)
+    custom_attributes = map(string)
+  })
+  default = null
+}
 variable "prefix" {
   description = "Prefix used to generate the bucket name."
   type        = string