When pod listing, filter out unschedulable and scheduler unprocessed pods not in the list of allowed schedulers

[damikag]

When pod listing, filter out unschedulable and scheduler unprocessed pods not in the list of allowed schedulers.

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR introduces new command line flag where a list of schedulers can be specified. If specified, cluster autoscaler will filter out pods not belong to those schedulers at the very beginning of the CA loop.

This feature is useful for customs CA configurations where CA does not intends to help pods targeting some custom schedulers. Specially in large clusters when there are thousands of unschedulbale pods which are not intended for CA, it adds unnecessary extra overheads and could affect CA decision making. This flag can be used as a mitigation for such cases.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

The flag should be set to empty for general release. This flag should only be used for specific clusters which have any such needs or as a mitigation tool if applicable.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: damikag
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[k8s-ci-robot]

PR needs rebase.

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