TLS 1.3 early data / 0-RTT

[drwetter]

This PR implements a check for TLS early data. It needs a compatible OpenSSL or LibreSSL version. For modern OS versions it should automagically pick the right, modern binary for the check.

Mitigations like Defer processing or HTTP 425 are not yet tested.

To clarify is

• [✓] whether to penalize SSLlabs rating (@magnuslarsen). testssl.net has it enabled but the Web UI claims it's not a/v, see https://www.ssllabs.com/ssltest/analyze.html?d=testssl.net&s=172.67.205.231&hideResults=on&latest
• [✓] Man pages
• [✓] Changelog

To be in line with other HAS2_* global vars (HAS2_QUIC, HAS2_UDS), the following vars were renamed from their OPENSSL2_HAS_* counter parts:

• HAS2_TLS13
• HAS2_CHACHA20
• HAS2_AES128_GCM
• HAS2_AES256_GCM

This fixes #1186.

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
• Update of other files

If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs, indentation is five spaces and any line endings do not contain any blank chars
• 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

[magnuslarsen]

whether to penalize SSLlabs rating

The rating guide does not specify anything about 0-RTT

A random selection of recent A+ scans all have 0-RTT disabled, so I think it is safe to assume it doesn't affect rating (yet anyway)

[drwetter]

@magnuslarsen : thanks for the clarification!

google.com (in my region) and cloudflare (testssl.net) have 0-RTT enabled, as the second openssl command clearly shows. The check @ SSLlabs is not correct . I haven't seen a host yet where that is correct.