Boil: Autodetect platform it builds on

[Maleware]

Current situation

If you build locally ( or on a builder ) you will need to specify your building platform if it is linux/arm64 as linux/amd64 is a default.

Defaulting happens silently and can lead to longer debugging sessions.

Ideal Situation

Boil should be able to autodetect the platform. Using --target-platform should be a override to the autodetection.

[NickLarsenNZ]

Agree. Intuitively, I'd expect it to know the default based on where it is run, rather than have a hard-coded default (that can of course be a fallback if detection somehow fails).

I assume there is a crate we can use that deals with the variety of ways to discover the platform.