Add a check to validate the changelog on PRs

[JorTurFer]

Proposal

Even it's documented the proper way to add entries in the changelog, there are cases where we still approve PRs with the entry unsorted or with other style errors.
It's difficult to review every thing without any error, but maybe we can create a bash script that checks the unreleased section to validate it and append it to pre-commit checks

Use-Case

No response

Anything else?

No response

[nitishchauhan0022]

/assing @JorTurFer can you please share the link for

Even it's documented the proper way to add entries in the changelog

[JorTurFer]

https://github.com/kedacore/keda/blob/main/CONTRIBUTING.md#Changelog