Support for CMEK/KMS key specification in GCENodeClass

[mdouek]

What would you like to be added:
Add support for specifying KMS encryption keys (CMEK) in the GCENodeClass CRD for boot disk encryption on Karpenter-provisioned nodes.

Why is this needed:
Organizations with GCP org policy constraints/gcp.restrictNonCmekServices cannot use Karpenter because node pool creation fails without a KMS key specified
Completion requirements:

This enhancement requires the following artifacts:

• Design doc
• API change
• Docs update

The artifacts should be linked in subsequent comments.

[jwcesign]

Hi, @mdouek Welcome to submit a PR to support this feature.