[MAINT]: Move VerifySignatureAsync into service or helper

[sommmen]

Describe the need

I'm not using the endpoint for webhooks, cause i have masstransit/rabbitMQ between receving and processing hooks.
I now copied the VerifySignatureAsync method over to my project, but making the signature validation a public api would be better.

SDK Version

No response

API Version

No response

Relevant log output

Code of Conduct

• I agree to follow this project's Code of Conduct

[github-actions]

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