Add option to pass custom filter funtion for nodes

[kisieland]

This will allow users to filter-out some of the nodes when filtering out pods potentially schedulable.

What type of PR is this?

/kind feature

What this PR does / why we need it:

Allows users to pass custom node filtering function to processor filtering out schedulable pods.

Special notes for your reviewer:

Does this PR introduce a user-facing change?

No

[k8s-ci-robot]

Hi @kisieland. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[aleksandra-malinowska]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aleksandra-malinowska, kisieland

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• cluster-autoscaler/OWNERS [aleksandra-malinowska]

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