[release-1.6] Default Ubuntu to 22.04 for new k8s versions

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #2807

/assign jackfrancis

Default Ubuntu to 22.04 for new k8s versions

[k8s-ci-robot]

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[CecileRobertMichon]

/hold

@jackfrancis @mboersma why the cherry-pick? This isn't a bug fix AFAICT

[mboersma]

This isn't a bug fix AFAICT

I agree overall, we should probably close these cherry-picks.

But...maybe it's better that all releases get the same distros for consistency? Otherwise, jobs based on release-1.6 will use Ubuntu 20.04 while newer jobs will use 22.04.

I'm not sure that's important, it's just the only argument I could think of besides "increased exposure for this code change."

[jackfrancis]

@CecileRobertMichon @mboersma I think I have a naive understanding of how this might work across our supported branches. By convention do we not backport the support of new k8s versions into our release branches?

[CecileRobertMichon]

I think it's okay to cherry-pick it if there is a strong argument to, but we should be extra diligent to add justification when cherry-picking something that is labeled as "kind/feature"

By convention do we not backport the support of new k8s versions into our release branches

This PR is not adding k8s version support, it's changing the default OS version

[mboersma]

it's changing the default OS version

Agreed, new k8s patches will still be supported on older branches. They'll just default to Ubuntu 20.04 whereas e2e on main and CAPZ's next release might use 22.04 for the same Kubernetes version. I don't think that's a problem on its own.

[jackfrancis]

@mboersma @CecileRobertMichon version support on older branches limited to 20.04 vs 22.04 is definitely (IMO) not a problem, so I'll close these cherry-pick PRs!