Allow specifying pixi global configuration

[hoxbro]

I would like to enable run-post-link-scripts = "insecure" in our CI. It would be easiest if this could be set directly in the action.

[pavelzw]

This would only work if we expose all global configuration endpoints.
A workaround for now would be to cat <<EOF the appropriate content to ~/.pixi/config.toml.
In general, I would be open to being able to provide a global configuration in setup-pixi

Something like this

uses: prefix-dev/setup-pixi@...
with:
  configuration: |
    run-post-link-scripts: "false"

[hoxbro]

That would also work.

[pavelzw]

I will eventually get to implementing it. If you want it quicker, I'm open for PRs as well.