feat: add enable_k8s_beta_apis support

[maikelpoot]

This PR will expose the enable_k8s_beta_apis:enabled_apis block of the google_container_cluster resource as a list of strings variable.

Example:

module "gke_cluster" {
  source     = "terraform-google-modules/kubernetes-engine/google//modules/beta-private-cluster"
  version    = "38.0.0"
  ...
  enable_k8s_beta_apis = [
    "networking.k8s.io/v1beta1/ipaddresses",
    "networking.k8s.io/v1beta1/servicecidrs"
  ]
  ...
 }

Tested as a local checkout against a cluster that had api's enabled with gcloud cli

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[apeabody]

Thanks for the contribution @maikelpoot!

[apeabody]

Please add to one of the existing examples (/examples) so this is covered by our tests.

[maikelpoot]

Damn, Just noticed i read your comment wrong, I added an additional test (by copying simple_regional_private to simple_regional_private_with_beta_apis) instead of adding it to an existing example.
Is that ok, or should i add it to the simple_regional_private example.

[apeabody]

Hi @maikelpoot! - It's fine to add as a new example, but more complex as that will need to be onboard as a test. In particular:

• A new ./test/fixtures to apply
• A new ./test/integration to validate
• Add the required apply, validate, teardown for the next example to ./build/int.cloudbuild.yaml
• Etc

Either direction you choose is fine.

[maikelpoot]

hi @apeabody,
As tempting as that sounds, i removed the extra example and applied the changes to the simple_regional_private example.

[apeabody]

Sounds good, you will need to pass a value for enable_k8s_beta_apis into the example fixture from here: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/blob/main/test/fixtures/simple_regional_private/example.tf

[maikelpoot]

Added a beta api to the default value of the fixture variable. As an empty default value doesn't test anything.

But this does mean that if this api is promoted within later k8s/gke version it could fail on this value.