feat: Set boot_disk_kms_key cluster wide and for cluster_autoscaling

[CPL-markus]

Currently it seems impossible to set KMS keys (boot_disk_kms_key) for the cluster autoscaler, which leads to node-pools being created using Google Managed Keys for all boot disks. As this is supported by the resource google_container_cluster, it should also be supported in the module.

Additionally similar to service_account the KMS key should be possible to be set cluster-wide as well.

[google-cla]

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[apeabody]

Thanks for the contribution @CPL-markus!

Please see the lint findings:

Working in ./modules/beta-autopilot-private-cluster ...
1 issue(s) found:

Warning: [Fixable] variable "boot_disk_kms_key" is declared but not used (terraform_unused_declarations)

  on variables.tf line 248:
 248: variable "boot_disk_kms_key" {

Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.7.0/docs/rules/terraform_unused_declarations.md

tflint failed ./modules/beta-autopilot-private-cluster 
Working in ./modules/beta-autopilot-public-cluster ...
1 issue(s) found:

Warning: [Fixable] variable "boot_disk_kms_key" is declared but not used (terraform_unused_declarations)

  on variables.tf line 248:
 248: variable "boot_disk_kms_key" {

Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.7.0/docs/rules/terraform_unused_declarations.md

tflint failed ./modules/beta-autopilot-public-cluster 

[apeabody]

/gcbrun

[apeabody]

/gcbrun

[apeabody]

Thanks for the contribution @CPL-markus!

Confirmed boot_disk_kms_key GA in TPG 5.25.0

[CPL-markus]

Thank you @apeabody for your support here!