Support decrypting HTTPS/TLS traffic via SSLKEYLOGFILE

[andreas-mausch]

Wireshark offers a way to decrypt HTTPS traffic via the environment variable SSLKEYLOGFILE and the Wireshark configuration (Pre)-Master-Secret.

See here for example.

I couldn't find a way to use it with termshark. If it already supports this feature, please ignore this issue.

I'd like to pass the log filename via a cli option to termshark.
termshark then uses the log file to decrypt TLS traffic the same way Wireshark does it.