Increase portability of zellij's config

[luccahuguet]

Increase portability of zellij's config

Daughter issue of https://github.com/luccahuguet/yazelix/issues/23

• have a zellij default config
• have a toml file with the things that make yazelix work (are there any?): yazelix.toml
• merge them both?
• create an install script that executes the previous steps for you?

if zellij has a more native way of doing so, that would be better