Add --stdio argument to Expert by default

[PJUllrich]

Closes #41

[MrSubidubi]

Thanks for this! Two minor things:

• Could we change this to unwrap_or_else instead and change the type of args on ExpertBinary to just Vec<String> (instead of the current Option<Vec<String>>?
• We usually do not fiddle with the arguments passed by users - if they set the arguments in their settings, we assume they know what they are doing and not change anything about what was passed (eventually we should have this probably, but we can currently not raise visibility for such things). Could we just pass them as-is without modifying these?

[PJUllrich]

@MrSubidubi done :) Thank you for the feedback!

If the user provides no arguments, we set them default to ["--stdio"] for the Expert language server:

* Binary: LanguageServerBinary {
    path: "~/Library/Application Support/Zed/extensions/work/elixir/expert-nightly/expert",
    arguments: [
        "--stdio",
    ],

[MrSubidubi]

Nice, thanks for the quick follow-up and congratulations to your first contribution! 🎉

[PJUllrich]

Whoohoo! Thank you very much :)