✨ KCP: default ControlPlaneKubeletLocalMode feature gate to true for >= 1.31.0

[sbueringer]

Signed-off-by: Stefan Büringer buringerst@vmware.com

What this PR does / why we need it:
This is now the proper fix to the issue discovered and mitigated (in e2e tests) in #10940

The underlying issue is the following

• Since we bumped our tests to Kubernetes 1.31 the "When testing Cluster API working on self-hosted clusters using ClusterClass with a HA control plane" test has been failing pretty frequently
• The root cause is that in some case a 1.31 kubelet tries to list services from a 1.30 apiserver
• This fails because the 1.30 apiserver does not support field selectors for spec.clusterIP: Field selector for Services based on ClusterIP and Type kubernetes/kubernetes#123905
• The problem is that kubeadm join configures the kubelet to use the apiserver loadbalancer instead of the local apiserver.
  With the feature gate enabled kubeadm should use the local apiserver endpoint instead

This PR now:

• enables the ControlPlaneKubeletLocalMode kubeadm feature gate per default for v1.31 Machines, if not otherwise specified by the user via the KCP object, by:
  • Defaulting the feature gate for the KubeadmConfigs we generate in KCP
  • Updating the kubeadm-config ConfigMap in workload clusters with defaulted feature gates (also via KCP)
• reverts the e2e test mitigation from 🌱 Enable kubeadm ControlPlaneKubeletLocalMode feature gate in e2e tests #10940

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]

/hold
still adding a few unit tests (and fixing the linter)

[sbueringer]

/test pull-cluster-api-e2e-main

[sbueringer]

/test pull-cluster-api-e2e-mink8s-main

[sbueringer]

cc @neolit123 @chrischdi @fabriziopandini

[sbueringer]

/test pull-cluster-api-e2e-main
/test pull-cluster-api-e2e-mink8s-main

e2e-main was green, e2e-main-mink8s timed out, but I think the cause of that is unrelated

[fabriziopandini]

/lgtm
/approve

/hold for @chrischdi to take a look

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 1018a7603fdde2240808f5735ca4779f42a6fa8a

[chrischdi]

/approve

/hold cancel

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrischdi, fabriziopandini

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[chrischdi]

/retest

MachinePool flake

[neolit123]

/lgtm
thanks @sbueringer for adding the CAPI integration!

[neolit123]

xref

• sig-cluster-lifecycle: best practices for immutable upgrades kubernetes/kubernetes#80774