Supports automatic deletion of instances when the limits of the NodePool is reduced

[daimaxiaxie]

Description

What problem are you trying to solve?

When I descrease the NodePool limits, the excess resources cannot be automatically deleted.

Case:

1. NodePool.limits.cpu = 512, It has 10 instances of 32C64G. cpu: 320
2. Set NodePool.limits.cpu = 256, I hope karpenter can automatically delete 2 instances.

How important is this feature to you?

This feature is useful when upgrading infrastructure.

Upgrading the image case:
NodePool A, NodeClass A, Image A.
NodePool B, NodeClass B, Image B.
Administrator controls the upgrade progress: descrease NodePool A limits, increase NodePool B limits; Eventually B completely replaces A.

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[k8s-ci-robot]

This issue is currently awaiting triage.

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