Add enable_confidential_nodes to safer-cluster

[morphf]

TL;DR

Add to Safer Cluster Module Inputs the option to enable_confidential_nodes.

Terraform Resources

https://registry.terraform.io/modules/terraform-google-modules/kubernetes-engine/google/latest/submodules/safer-cluster

Detailed design

No response

Additional information

Confidential Nodes are GA about 1.5 years.
Safer Cluster module is a easy-to-use abstraction for better security defaults.
So it only makes sense that it will be an available input for safer-cluster module.

[github-actions]

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