[FR]: Add upgrade notification_config filter option in gke-cluster modules

[hvnayak]

The feature request

Currently, gke-cluster-autopilot and gke-cluster-standard modules are missing the option to filter the cluster upgrade notifications and by default all types of upgrade notifications are sent.

Proposed solution

Added filter option to notification_config's pubsub block of gke-cluster-autopilot and gke-cluster-standard modules

Additional context

Even though, upgrade notifications can be filtered at Pub/Sub or cloud run function but that won't make much sense because of the additional configuration and undelivered messages cost. Also, filtering notifications in GKE is strongly recommended by Google over filtering in Pub/Sub because of the ease-of-use and because users are billed only for the notifications they receive.

• https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/container_cluster#filter-1
• https://cloud.google.com/kubernetes-engine/docs/concepts/cluster-notifications