Audit Kubernetes version specific code

[sbueringer]

Goal of this issue is to audit all code in core Cluster API for Kubernetes version-specific handling and come up with an overview with which Kubernetes (and estimated Cluster API) version we can drop which code.

Tasks:

• Audit all code

Overview

Code removed with Cluster API v1.11

PRs:

• ⚠️ Cleanup version handling of unsupported Kubernetes releases #12303

Code:

• KCP: Remove cgroup driver handling in KCP (-v1.23)
• KCP: Webhook validation code to block update to (v1.19)
• KCP: Webhook validation code for registry migration (v1.22-v1.25)
• test/extension: Remove cgroup driver handling (-v1.23)
• test/framework: Remove handling for nodeRoleOldControlPlane

Code required for workload clusters

Note: We are going to keep the code 2 Cluster API versions longer as we don't strictly enforce the Kubernetes version support range (https://main.cluster-api.sigs.k8s.io/reference/versions#core-provider-cluster-api-controller)

v1.28

• Remove https://github.com/kubernetes-sigs/cluster-api/blob/main/test/e2e/clusterctl_upgrade.go#L728-L735
• CRS: drop ensureKubernetesServiceCreated (CRS controller should wait for the 'kubernetes' service ready before reconciling CRS objects #7804 (comment)) (replacement feature GA + 2)

v1.29

• KCP: Remove AllowClusterAdminPermissions

v1.30

• Remove handling of kubeadm v1beta3 types in CABPK / KCP

TBD

• Remove handling for ControlPlaneKubeletLocalMode feature gate
• Remove old versions in CAPD kind mapping

Code related to management clusters

v1.32

• When v1.32 (?) is our min supported mgmt cluster version we should replace some of our Pattern validation with CEL (e.g. RFC 1123 label/subdomain): ⚠️ Restructure classRef field in Cluster.spec.topology #12235 (comment) (helps to avoid mistakes in the regexp patterns) => Let's verify that additionally with a manual test

v1.34

• When v1.34 (?) is our min supported mgmt cluster version we should evalute if we can use k8s-short-name and k8s-long-name (Introduce OpenAPI format support for k8s-short-name and k8s-long-name kubernetes/kubernetes#132504)

/kind cleanup

[sbueringer]

I intentionally added this to the v1.5 milestone as we won't start this activity before then and it would be good to have for v1.5

[fabriziopandini]

/triage accepted
/help

[sbueringer]

/remove-help

I'll be working on this one