🌱 ClusterClass: add ref and controlPlane name builtin variables

[sbueringer]

Signed-off-by: Stefan Büringer [email protected]

What this PR does / why we need it:
While writing ClusterClasses for CAPZ, we discovered that additional builtin variables are needed.

CAPZ has a controller which generates secrets which are eventually used for Machines. These secrets then have to be configured in KCP.spec..kubeadmConfigSpec and in KubeadmConfigTemplates.

The secrets are generated with the names of the corresponding current AzureMachineTemplates. So essentially CAPZ has to be able to take the name of the currently referenced AzureMachineTemplate of KCP/MD and then patch KCP / the KubeadmConfigTemplate accordingly.

To make this possible we introduce builtin variables for all references in KCP / MD.

We additionally add builtin.controlPlane.name because it seems to be a good variable to have.

For additional context, please see this Slack thread: https://kubernetes.slack.com/archives/CEX9HENG7/p1645731252682719

The plan is to cherry-pick this PR to release-1.1 too. This way it will be possible to experiment
with CAPZ ClusterClasses after the next CAPZ and CAPI core release.
This does not block the CAPZ release (because the next CAPZ release won't include cluster-templates using ClusterClasses)

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[sbueringer]

/cc @CecileRobertMichon @enxebre @fabriziopandini @vincepri @shysank

/cherry-pick release-1.1

[k8s-infra-cherrypick-robot]

@sbueringer: once the present PR merges, I will cherry-pick it on top of release-1.1 in a new PR and assign it to you.

In response to this:

/cc @CecileRobertMichon @enxebre @fabriziopandini @vincepri @shysank

/cherry-pick release-1.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[sbueringer]

Tested it locally with my limited CAPZ knowhow. Looks like it works, e.g. KCP:

      files:
      - contentFrom:
          secret:
            key: control-plane-azure.json
            name: my-azure-cluster-control-plane-hqc7h-azure-json
...
    machineTemplate:
      infrastructureRef:
        apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
        kind: AzureMachineTemplate
        name: my-azure-cluster-control-plane-hqc7h
        namespace: default

[sbueringer]

/test pull-cluster-api-e2e-full-main
/test pull-cluster-api-e2e-workload-upgrade-1-23-latest-main

[fabriziopandini]

only one nit

[shysank]

Tested it locally, it works. Thanks @sbueringer !

[fabriziopandini]

/lgtm
@killianmuldoon if you can give another pass

[fabriziopandini]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini

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[k8s-infra-cherrypick-robot]

@sbueringer: new pull request created: #6215

In response to this:

/cc @CecileRobertMichon @enxebre @fabriziopandini @vincepri @shysank

/cherry-pick release-1.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.