Allow whitelisted `sudo` alternatives

[rami3l]

... in the future I could possibly make sudo -S replaceable with something else via the config (env var + cli args + config file).

This might include:

• gsudo on Windows: should work fine since the interactivity is implemented via a pop-up window.
• doas on *nix: might require working around the lack of sudo -S, see https://github.com/Duncaen/OpenDoas/issues/21#issuecomment-854727152.
• run0: https://news.itsfoss.com/systemd-run0

Originally posted by @rami3l in https://github.com/rami3l/pacaptr/issues/2#issuecomment-1782247456