fix: Ensure correct architecture containerd/runc is downloaded

[thefirstofthe300]

Change description

The current arm64 implementation for Flatcar is half-baked, mainly due to the containerd and runc binaries being downloaded for the wrong architecture.

This PR makes an attempt to better automatically detect the OS and architecture of the machine during the installation of those two binaries.

I have tested both the amd64 and arm64 installation paths in AWS. I don't have access at work to any other cloud provider so I haven't been able to test elsewhere.

[k8s-ci-robot]

Hi @thefirstofthe300. Thanks for your PR.

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[k8s-ci-robot]

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[mboersma]

/ok-to-test

[thefirstofthe300]

/retest

[thefirstofthe300]

/retest