Stricter kubeadm validation (config and runtime checks)

[VannTen]

What type of PR is this? /kind cleanup

What this PR does / why we need it: This makes kubespray stricter regarding kubeadm config and errors in 2 ways:

1. validate the kubeadm config files on templating
2. don't ignore preflight errors by default. Instead we expose a variable to let users ignore certain errors if needed.

We need this in order to catch bad formatting of the config files (which are otherwise non-fatal), which could led to settings not applied at all.

Also some cleanups, and fix some stuff introducted in v1beta4 support #11674 (not caught because of the lack of that validation, precisely)

Special notes for your reviewer: Apparently, we ignore kubeadm errors since the introduction of kubeadm support in #1631 (commit 6da20e2

Does this PR introduce a user-facing change?:

action required
`kubeadm_ignore_preflight_errors` is introduced to ignore specific preflight checks from kubeadm. The previous was effectively `all`, so some errors might surface during upgrade, in which cases, users should add the ones they choose to ignore to that variable.

[VannTen]

/ok-to-test

[VannTen]

Well, the validation works:

TASK [kubernetes/kubeadm : Create kubeadm client config] ***********************
task path: /builds/kargo-ci/kubernetes-sigs-kubespray/roles/kubernetes/kubeadm/tasks/main.yml:74
fatal: [test-vm-gv46p]: FAILED! => {"changed": false, "checksum": "562a882839726dd23f5de3de823925aa2f7ca942", "exit_status": 1, "msg": "failed to validate", "stderr": "error unmarshaling configuration schema.GroupVersionKind{Group:\"kubeadm.k8s.io\", Version:\"v1beta4\", Kind:\"JoinConfiguration\"}: strict decoding error: unknown field \"discovery.timeout\"\nTo see the stack trace of this error execute with --v=5 or higher\n", "stderr_lines": ["error unmarshaling configuration schema.GroupVersionKind{Group:\"kubeadm.k8s.io\", Version:\"v1beta4\", Kind:\"JoinConfiguration\"}: strict decoding error: unknown field \"discovery.timeout\"", "To see the stack trace of this error execute with --v=5 or higher"], "stdout": "", "stdout_lines": []}

[VannTen]

I'm not sure why the vagrant job is still failing, the v1beta4 should be fixed there as well :thinking:

I had missed one.

{
  "changed": false,
  "checksum": "387f5d5b7358fd92b61070db17c06edd4e56827e",
  "exit_status": 1,
  "msg": "failed to validate",
  "stderr": "error unmarshaling configuration schema.GroupVersionKind{Group:\"kubeadm.k8s.io\", Version:\"v1beta4\", Kind:\"JoinConfiguration\"}: strict decoding error: unknown field \"discovery.timeout\"\nTo see the stack trace of this error execute with --v=5 or higher\n",
  "stderr_lines": [
    "error unmarshaling configuration schema.GroupVersionKind{Group:\"kubeadm.k8s.io\", Version:\"v1beta4\", Kind:\"JoinConfiguration\"}: strict decoding error: unknown field \"discovery.timeout\"",
    "To see the stack trace of this error execute with --v=5 or higher"
  ],
  "stdout": "",
  "stdout_lines": []
}

[VannTen]

/cc @tico88612

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: MrFreezeex, tico88612, VannTen

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