feat: use non-root user for base-image

[moolen]

There is no need to use the root user. This allows the user to comply with pod security standards.

It turns out that the nonroot image has the cwd set to /home/nonroot whereas latest is rooted in / 🤷 .
This is important because the helm chart uses ./cluster-autoscaler as command. Keeping the same cwd seems like the safest option to me.

Which component this PR applies to?

cluster-autoscaler

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR makes infosec happy 😃

Which issue(s) this PR fixes:

Fixes #3705

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[maltejk]

Is there something left to do on this?

[moolen]

Hey @maltejk 😁! Actually i need to set the uid to make it work. I'll commit that later and mark the pr as ready.

[moolen]

/assign @feiskyer

[moolen]

@feiskyer did you find some time to look into this yet?

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/lifecycle stale

[feiskyer]

sorry, didn't notice this PR

the changes LGTM

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: feiskyer, moolen

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