Buildx/Multi-Arch Support

[heywoodlh]

Request

I'm not sure if this is already supported but it'd be awesome to use docker-template to build for multiple architectures. Perhaps using something like the Docker buildx plugin would be best.

I'm not a Ruby user at all and only discovered docker-template today when attempting to build jekyll's Docker image on my M1 Macbook, but if I could use docker-template to build cross-architecture builds I would absolutely use docker-template for my personal projects.

Examples

Something like this would be really awesome:

docker-template buildx --platform linux/amd64,linux/arm64,linux/armhf ...

Anyway, not sure if this is all that feasible but if it was possible it would probably make things easier for users of docker-template to be able to deploy for more than one platform (unless it's already possible and I just missed it in the documentation).

Thanks for a super cool tool and any time spent looking at this request!