Implement `namespaceSelector` for Pod (anti)affinity when considering NodeFit

[logyball]

This is a follow up from the comment here, which contains a ton more context.

Is your feature request related to a problem? Please describe. For the nodeFit feature, it has begun considering pod anti-affinity when determining if a pod fits on a node. Pod anti-affinity can include the namespace, but it can also utilize namespaceSelector to find namespaces logically rather than explicitly.

Describe the solution you'd like

Also consider namespaces matched by namespaceSelector.

Describe alternatives you've considered

Do not implement this feature. Thus far it hasn't created a problem, as I believe namespaceSelectors are not widely used.

What version of descheduler are you using?

descheduler version: v0.28.1

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