KubeadmControlPlane spec.kubeadmConfigSpec.joinConfiguration.patches.directory should be mutable

[superbrothers]

User Story

As an operator I would like to be able to modify KubeadmControlPlane spec.kubeadmConfigSpec.joinConfiguration.patches.directory.

Detailed Description

I want to update the spec of apiserver of the existing cluster, but changes to this field are not permitted currently.

The KubeadmControlPlane "eval-control-plane" is invalid:
* spec.kubeadmConfigSpec.initConfiguration.patches.directory: Forbidden: cannot be modified
* spec.kubeadmConfigSpec.joinConfiguration.patches.directory: Forbidden: cannot be modified

Anything else you would like to add:

None

/kind feature

[sbueringer]

@superbrothers Sounds good to me.

To implement this we have to:

• add patches to allowedPaths like e.g. nodeRegistration:

  cluster-api/controlplane/kubeadm/api/v1beta1/kubeadm_control_plane_webhook.go

  Lines 144 to 145 in 062883d

  	{spec, kubeadmConfigSpec, initConfiguration, nodeRegistration, "*"},
  	{spec, kubeadmConfigSpec, joinConfiguration, nodeRegistration, "*"},

• add a corresponding unit test (there are already a lot of similar unit test cases)

[superbrothers]

@sbueringer Thanks for your quick comment. I'll implement it.

[superbrothers]

@sbueringer I've created a PR.