Add arm64 architecture support to the OS testing matrix

[twz123]

Is your feature request related to a problem? Please describe.

Currently, only the x86_64 architecture is tested.

Describe the solution you would like

Also add support for arm64. Most (all?) OSes in the test matrix also have official arm64 AMIs available. K0s is already tested on arm64 in CI and during the release pipeline. Might make sense to also have this in the OS tests.

Describe alternatives you've considered

Don't support arm64. That'd be a new dimension and there'd be a bit of a combinatorial explosion.

Additional context

We cloud also opt to add support for the architecture, but not to add it to the nightly testing matrix selection. That way, we'd keep the combinations a bit lower, but could still trigger it on demand.

[kke]

Of the official images at docker hub, ArchLinux and Clearlinux are not available for arm.

Judging from the issues for k0s and k0sctl I've seen, I think we should probably also test on Rocky and maybe Arch. It would be great to test on Flatcar, but setting it up, at least for our test suite, is non-trivial.

[twz123]

I'm talking about the AWS based tests on VMs. Rocky and Flatcar are already in the matrix.

Those tests are currently relying on officially published AMIs, but Arch doesn't ship any. At least not a few months ago, when I last checked. Dunno about Clearlinux.