Fix cluster autoscaler permissions

[voelzmo]

How to categorize this PR?

/area auto-scaling
/kind bug

What this PR does / why we need it
Adjust permissions for cluster-autoscaler, such that we don't see any error messages anymore and we can make use of expander: priority. At the same time, I reduced the scope of permissions for ConfigMaps, as the cluster-autoscaler only needs access to the kube-system namespace.

Which issue(s) this PR fixes:
Fixes #6370

Release note:

Fixed a bug that prevented Shoots from being able to use `expander: priority` for cluster-autoscaler

[himanshu-kun]

/lgtm
Thanks for the changes, I also think a role seperately for kube-system is better.
I have a concern/doubt though, upstream I see they still have configmap rules in ClusterRole. Maybe they forgot to update it

[gardener-prow]

@himanshu-kun: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

/lgtm
Thanks for the changes, I also think a role seperately for kube-system is better.
I have a concern/doubt though, upstream I see they still have configmap rules in ClusterRole. Maybe they forgot to update it

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[ialidzhikov]

/lgtm
/approve

[gardener-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: himanshu-kun, ialidzhikov

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