fix: Create new node pool when shielded_instance_config changes

[abursavich]

Fixes #923

This adds the enable_secure_boot and enable_integrity_monitoring properties from the shielded_instance_config to the list that triggers the creation of a new node pool.

Example:

...

      ~ node_config {
          ~ shielded_instance_config {
              ~ enable_secure_boot          = false -> true # forces replacement
                # (1 unchanged attribute hidden)
            }
        }

...

│ Error: resource - projects/xxx/locations/us-west1/clusters/xxx/nodePools/xxx-00de - already exists
│ 
│   with module.gke.google_container_node_pool.pools["xxx"],
│   on .terraform/modules/gke/modules/beta-private-cluster-update-variant/cluster.tf line 448, in resource "google_container_node_pool" "pools":
│  448: resource "google_container_node_pool" "pools" {
│ 

See: ForceNew at https://github.com/hashicorp/terraform-provider-google/blob/v4.19.0/google/node_config.go#L208-L233

[abursavich]

I can't view any details of the kubernetes-engine-int-trigger failure?

[comment-bot-dev]

@abursavich
Thanks for the PR! 🚀
✅ Lint checks have passed.

[bharathkkb]

Thanks for the PR @abursavich