helm: manage CoreDNS addon as Helm chart

[burgerdev]

Context

We're still in the process of moving CoreDNS from cluster addon to Helm chart. Prior art:

1. helm: manage CoreDNS addon as Helm chart #3236 introduced the Helm chart
2. helm: fix kubeadm bugs caused by CoreDNS installation #3353 fixed some bugs
3. helm: revert parts of CoreDNS Helm chart packaging #3366 reverted everything except upgrade-agent support

Now that we released 2.18, we can reapply the changes.

Proposed change(s)

• Reapply the reverted changes.

Additional info

• AB#4681

Checklist

• Run the E2E tests that are relevant to this PR's changes
  • Upgrade test from v2.18.0
  • e2e test
  • Manual upgrade test starting from this PR
• Add labels (e.g., for changelog category)
• Is PR title adequate for changelog?
• Link to Milestone

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Coverage report

Package	Old	New	Trend
bootstrapper/internal/kubernetes	37.70%	37.60%	↘️
bootstrapper/internal/kubernetes/k8sapi	11.80%	11.80%	🚧
cli/internal/cmd	41.10%	41.10%	🚧
internal/constellation	18.60%	18.50%	↘️
internal/constellation/helm	33.60%	34.50%	↗️
internal/constellation/helm/corednsgen	0.00%	0.00%	🆕
internal/kubernetes/kubectl	6.90%	8.20%	↗️
terraform-provider-constellation/internal/provider	3.50%	3.50%	🚧