Do not use static certificates for diagnose tests

[stevendpclark]

Description

The static x509 certificate is expiring Jan 6 2025 and is now causing test failures within the diagnose test cases.

Instead of just reissuing the certificate and having to deal with this in the future, codify the generation of certificates and test cases that we want to validate so the certificates will never expire again.

For time reasons, I haven't fixed all the test cases, mainly the ones that were causing issues for now.

VAULT-32989

TODO only if you're a HashiCorp employee

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• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
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• RFC: If this change has an associated RFC, please link it in the description.
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  description. Also, make sure the changelog is in this PR, not in your ENT PR.

[github-actions]

CI Results:
All Go tests succeeded! ✅

[github-actions]

Build Results:
All builds succeeded! ✅

[victorr]

Awesome, thanks for fixing the tests!

[victorr]

Very good.

Again, thank you for making testing with certificates better.