[8.x](backport #41542) Switch to base 16 for TLS serial number in packetbeat in line with ECS changes

[mergify[bot]]

Proposed commit message

This switches the serial_number field in packetbeat's TLS reporting to use base 16 values instead of base 10:

        "public_key_size":             "2048",
        "serial_number":               "1121E97D5D37348C572C555A3A59B7B65D2B",
        "signature_algorithm":         "SHA256-RSA",

I don't think this is a breaking change? Also note the lack of a 0x indicator. Not sure if we care.

ECS PR here: https://github.com/elastic/ecs/pull/2383

Also note that this maintains the liter bypass for dsa, which is deprecated. Do we still need it?

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

This will alter the reported serial_number for TLS certs from base 10 to base 16.

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This is an automatic backport of pull request #41542 done by Mergify.

[botelastic[bot]]

This pull request doesn't have a Team:<team> label.

[mergify[bot]]

This pull request is now in conflicts. Could you fix it? 🙏 To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b mergify/bp/8.x/pr-41542 upstream/mergify/bp/8.x/pr-41542
git merge upstream/8.x
git push upstream mergify/bp/8.x/pr-41542

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @fearful-symmetry? 🙏