chore: minor refactor to reduce copy/paste code in ScaledObject webhook

[wozniakjan]

all in the title :) intending to merge after 2.13.0 release so keeping as draft for now

Checklist

• [X] I have verified that my change is according to the deprecations & breaking changes policy
• [X] Changelog has been updated and is aligned with our changelog requirements
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Fixes #5397