Allow using the system openssl version

[theoparis]

I was going to PR a simple change for this but I decided to create a discussion here first:

Since I prefer using AWS-LC which has better QUIC support and other various improvments, I tried to cargo install zellij but was given an error relating to perl dependencies which means zellij is trying to compile openssl from source. The only change needed to make this work better would be move the vendored feature from zellij-utils to the root crate. Then it can toggled on via something like cargo install zellij --features vendored-ssl.

Related: theoparis@5e879dd