Add a few extension numbers in the server hello

[drwetter]

Issue #2686 showed a server which listed an unknown extension number from RFC 8446. THis PR adds this number and a few (later) ones.

It just lists them when detected in parse_tls_serverhello()

See also https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml

What is your pull request about?

• Bug fix
• Improvement
• New feature (adds functionality)
• Breaking change (bug fix, feature or improvement that would cause existing functionality to not work as expected)
• Typo fix
• Documentation update
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If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs and the indentation is five spaces
• I've read CONTRIBUTING.md and Coding_Convention.md
• I have tested this fix or improvement against >=2 hosts and I couldn't spot a problem
• I have tested this new feature against >=2 hosts which show this feature and >=2 host which does not (in order to avoid side effects) . I couldn't spot a problem
• For the new feature I have made corresponding changes to the documentation and / or to help()
• If it's a bigger change: I added myself to CREDITS.md (alphabetical order) and the change to CHANGELOG.md