[SSL] Link to alternative CT search tool

[rellem]

Summary

crt.sh is a great resource, but it seems to have server issues quite often so a backup link could be useful.

Disclosure: I'm the founder of CertObserver.

Documentation checklist

• The change adheres to the documentation style guide.

[cloudflare-docs-bot]

Review

✅ No issues found in commit ac98ee6.

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[baubuchon-cf]

Hey rellem, thanks for the PR and for calling out the CertObserver connection up front.. I appreciate that.

Going to close this one though. This isn't a reflection on CertObserver, we just don't want to start adding vendor-specific links to our docs on a case by case basis.

If crt.sh downtime turns into a real recurring problem, we can revisit with more general wording. Thanks for contributing.

[rellem]

I understand. Thanks for letting me know!