Test exclusive TLS 1.3

[lhoguin]

We should run tests with TLS 1.3 enabled exclusively. Exclusive TLS 1.3 rejects some options and operates differently than when used in combination with other TLS 1.x versions.

[zuiderkwast]

Related to #1621.

A test was added in that PR but it was later removed. Do we need a test? If yes, should we run lots of test with this config or just one test case?

[essen]

Honestly considering the future is TLS 1.3 and the future is here(tm) I think the right approach would be to update the tests to use exclusively TLS 1.3 instead of 1.2. But I'm not sure the TLS 1.3 support was perfect in OTP-24+ which is what the next Cowboy release will target, so this ticket might be deferred.

The release after that will include experimental HTTP/3 which itself uses TLS 1.3 so it might be a better time to do the switch.

[essen]

OK let's wait for when we are 25 or 26+ and just convert the TLS tests to use exclusive 1.3.