Better control for Critical Pods

[AndresPineros]

Right now the control to mark pods as critical is very basic and requires doing changes in many pods' annotation.

Proposal 1 - Non-critical annotation
If I have 100 pods but I want the descheduler to consider "non-critical" only 20, that means I have to add annotations to 80 pods. We could have a "non-critical" annotation to only mark 20 pods. This could be controlled with an argument. --non-critical-pod-matcher=true (default false).

Proposal 2 - Consider current labels as critical
If I already have an annotation in my running applications that I know identifies a set of critical pods, it would be nice to be able to say "Pods with this custom annotation and value are considered critical". With this, no changes would have to be applied at all to make descheduler run. Personally, I have an annotation called "layer" with values (backend|monitoring|data|frontend). I consider my data and monitoring Pods critical, if I already have this annotation, why add another?

It could be done with --extra-critical-annotations="layer=data,layer=monitoring,k8s-app=prometheus" . And if --non-critical-pod-matcher is set to true, then --extra-non-critical-annotations="...."

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