feat: Implement support for SSLKEYLOGFILE

[duesee]

See https://www.ietf.org/archive/id/draft-thomson-tls-keylogfile-00.html

[duesee]

Adding ...

// Allow using SSLKEYLOGFILE.
config.key_log = Arc::new(rustls::KeyLogFile::new());

... to the TLS config, and setting the SSLKEYLOGFILE=<path> environment variable will create the secret log file.

Wireshark: Go the "Preferences.../Protocols/TLS" and set the "(Pre)-Master-Secret log filename". This way, Wireshark can decrypt encrypted TLS records.