fix: update broken Contribute links and redirects

[codeEvolveZenith345]

This PR updates all broken "Contribute" links and redirection rules throughout the documentation and config files to point to the official Knative contributor guide. Prevents 404 errors and improves developer onboarding.

Proposed Changes

• Updates /contributing/ redirects and documentation links to use https://knative.dev/community/contributing/
• Fixes internal and external navigation for contributors
• Improves overall developer experience and documentation quality

Fixes #6483

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The committers listed above are authorized under a signed CLA.

• ✅ login: codeEvolveZenith345 / name: codeEvolveZenith345 (634b690, 65f8668, 69c5309, 797fb5d)

[knative-prow]

Welcome @codeEvolveZenith345! It looks like this is your first PR to knative/docs 🎉

[evankanderson]

I think the redirects should stay same-site, rather than hard-coding the hostname part of the URL -- this allows us to check out the behavior on previews, like

https://deploy-preview-6484--knative.netlify.app/docs/contributing/about

(Oddly, this redirect still works -- so it may be that something else is overwriting the hostname in the redirect map.)

[evankanderson]

/assign

[evankanderson]

Making the the "use host-relative paths" suggestion as suggested edits.

[codeEvolveZenith345]

hey @evankanderson
I am grateful for the review and commit-suggestion, I have implemented the suggestions,
The PR is ready to be merged!

Thank you.

[evankanderson]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: codeEvolveZenith345, evankanderson

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