Update Startup boost AEP after API review

[kamarabbas99]

What type of PR is this?

/kind documentation
/kind feature

What this PR does / why we need it:

Seperate AEP changes form feature PR. #9141 (comment)

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

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

- [KEP]: (https://github.com/kubernetes/autoscaler/tree/master/vertical-pod-autoscaler/enhancements/7862-cpu-startup-boost#aep-7862-cpu-startup-boost)

[k8s-ci-robot]

Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: kamarabbas99
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[omerap12]

/lgtm
/assign @adrianmoisey