Dynamic namespace filtering

[yann-soubeyrand]

What would you like to be added:

It could be great to have an option to dynamically filter the namespaced resources.

Why is this needed:

Having a static namespaces option is good, but it forces one to re-configure KSM each time metrics for a new namespace are needed.

Describe the solution you'd like:

I’d like to be able to configure a namespace label selector, so that KSM can dynamically discover namespaces based on labels and emit metrics only for objects in these namespaces.

Additional context:

[k8s-ci-robot]

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