Auto discovery default certificate and certificate list

[abeowlu]

Issue

#4090

Description

AWS ELB API ignores the default certificate when certificate list is provided in TLS negotiation.
The auto discovered default certificate is needed for TLS negotiation. Adding the default certificate discovered to the extre certificate list

brief logic change:

• add default certificate to extraCert list as AWS ELBs ignores default certificate in certain SNI TLS negotiation scenario
• TODO discussion: accept user specified default certificate - skipping as certificate-arn implements similar functionality, and that logic shortcircuits auto-discovery execution

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: abeowlu
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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: abeowlu / name: Abraham Olu (0320065, 435ded0, 79b0c32, 7e09e62, b36e823)

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