add option to disable opam sandboxing

[sykhro]

It would be useful to have an option to init opam with the --disable-sandboxing flag, allowing this action to be used inside docker containers

[avsm]

That sounds useful. Out of interest, can you use this action within a GH Action in Docker mode, or is this for running the action locally?

[sykhro]

Running this in Docker on GH Actions I couldn't get past the opam init

[smorimoto]

@avsm If you agree with this idea, I will add an implementation for this. Well, it will be implemented as an input only available on Ubuntu and macOS, as there is no option other than disabled on Windows.

[smorimoto]

This will be supported in the next version.

[Risto-Stevcev]

+1 on this, would be really useful for testing locally

[smorimoto]

The functionality that allows us to do this will finally be introduced in v2.

[smorimoto]

https://github.com/avsm/setup-ocaml/blob/v2/examples.md#using-with-containers