Add python example for signature validation on secret scanning notifications

[ckuethe]

Why:

The secret scanning workflow documentation (https://docs.github.com/en/enterprise-cloud@latest/developers/overview/secret-scanning-partner-program#implement-signature-verification-in-your-secret-alert-service) doesn't have example validation in python. I found at least two other people asking about how to do this in python with no answers.

Fixes #18778

What's being changed:

Added two different ways to validate the signature; one uses Cryptodome (https://pycryptodome.readthedocs.io/en/latest/) and the other uses python-ecdsa (https://github.com/tlsfuzzer/python-ecdsa)

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  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

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[github-actions]

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Content directory changes

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Source	Preview	Production	What Changed
developers/overview/secret-scanning-partner-program.md	fpt ghec	fpt ghec

[janiceilene]

@ckuethe Thanks so much for opening a PR! I'll get this triaged for review ✨