k8s: add 1.29, remove 1.26, default 1.28

[malt3]

Context

Add support for k8s 1.29 and move versions accordingly.

Proposed change(s)

• k8s: add 1.29, remove 1.26, default 1.28

Additional info

• Changelog
• e2e test Azure
• e2e test GCP
• e2e test AWS
• e2e upgrade

Checklist

• Update docs
• Add labels (e.g., for changelog category)
• Is PR title adequate for changelog?
• Link to Milestone

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[github-actions]

Coverage report

Package	Old	New	Trend
internal/versions	9.70%	9.70%	🚧

[msanft]

Code changes LGTM, did we check the kubeadm admin-conf change? Didn't look into it in too much detail, but this sounds like something that might trickle down to our kubeadm usage?

[malt3]

[...] did we check the kubeadm admin-conf change?

Yes. I tested this and also looked this up in our code: we generate the constellation-admin.conf based on a separately created x509 key, that will still be part of the system:masters group.

[elchead]

lgtm. should we cover an upgrade test from 1.28 to 1.29?

[malt3]

should we cover an upgrade test from 1.28 to 1.29?

Will do!

EDIT: the pipeline cannot test this automatically, since it needs to first upgrade from 1.27 to 1.28 and then from 1.28 to 1.29.
I tested this manually instead.