docs Docs: Improve and expand on webhook signature testing

Description

This PR cleans up and expands the documentation on webhook signature testing to recommend better, more accessible tools. Key Changes:

Expanded Tooling: Added a segment for local testing/inspection tools and cloud-based webhook testing services.
New Recommendations: Replaced RequestBin with Webhook.site and Beeceptor for instant, zero-setup testing endpoints. RequestBin requires account creation, which adds multiple steps.
Clarity: Improved grammar to be more descriptive and professional.

That aside, I noticed that the link on step 2 [Configure](#configure) points to an anchor URL that doesn't exist. I have left it untouched.

Checklist

[x] Commits have been rebased.
[x] Linting has been run against the changed file(s).
[x] The PR adheres to the writing style guide and contribution guide.

Nov 01 '25 19:11 bee-anvith

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Nov 01 '25 19:11 coderabbitai[bot]

Just following up on the status of #2936. Let me know if there's anything else needed from my end.

Nov 11 '25 05:11 bee-anvith