Allow global install

[olivier-lacroix]

It would be useful if setup-pixi allowed the installation of global executables (ie like pixi global).

This could either be by referring to a global manifest, or maybe providing a list of package to pass to global install for simpler cases.

This could offer better options than existing specialised GH actions. For instance, setup-gcloud does not support caching natively, and take a fair bit of time (20s).

[olivier-lacroix]

This could help address, amongst other use cases, #126

[looooo]

I have also a use-case. Would be nice if pixi global would be supported.

[pavelzw]

how would you imagine the API looks like in this case and what should and should not be cached?