Enhance the scalability of multi-type workloads

[chenzhiguo]

Describe the feature

Currently, KPA natively supports automatic scaling for workloads like Deployment. However, many large enterprises have their own developed types of workloads, such as the open-source CloneSet or mine AppSet. At this point, Knative has some shortcomings in scalability when facing different types of workloads. There is a hope to enhance scalability in this regard.

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[dprotaso]

Cross posting what I said on the PR #15529 (comment)

Hey just catching up here - I think the right implementation we want to use is the /scale subresource.

This would allow us to work with any k8s type that can be scaled (ideally without modifications to the autoscaler.

https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#subresources

@chenzhiguo is this something you'd be interested in continuing?