fix: Handle placeholder instance decommission safely in AWS ASGs

[ruiscosta]

Merge branch 'fix/aws-asg-placeholder-decommission'

This merge resolves an issue in the Kubernetes Cluster Autoscaler where actual instances within AWS Auto Scaling Groups (ASGs) were incorrectly decommissioned instead of placeholders. The updates ensure that placeholders are exclusively targeted for scaling down under conditions where recent scaling activities have failed. This prevents the accidental termination of active nodes and enhances the reliability of the autoscaler in AWS environments.

Key improvements include:

• Refined logic to strictly identify unsuccessful scaling activities.
• Ensured that scaling operations affect placeholders only, preventing unintended impacts on real instances.
• Expanded unit tests and validations to bolster the resilience and correctness of the scaling process.

Fixes #5829

What type of PR is this?

/kind bug

What this PR does / why we need it:

This PR prevents the Kubernetes Cluster Autoscaler from erroneously decommissioning actual nodes during scale-down operations in AWS environments, which could lead to unintended service disruptions.

Which issue(s) this PR fixes:

Fixes #5829

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Fix an issue in the Kubernetes Cluster Autoscaler where actual AWS instances could be incorrectly scaled down instead of placeholders.

[k8s-ci-robot]

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• fb69323 fix: Handle placeholder instance decommission safely in AWS ASGs

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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

Hi @ruiscosta. Thanks for your PR.

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