ENH: Support pass-through options to container engine (Docker or Podman)

[jeliker1]

Please add option to pass container engine directives/arguments. For example:

fn build --container-arg platform=linux/amd64

This specific issue arose when trying to cross-compile on macOS with Apple CPU but output platform is amd64. Docker allows environment variable DOCKER_DEFAULT_PLATFORM=linux/amd64 but Podman doesn't have an equivalent. Instead of relying on container engine options to override default command-line directives, allow me to pass through any number of container engine directives e.g.

• --platform
• --arch
• --all-platforms

…and so on using my example such as (forgive the poor example of setting both platform and arch)

fn build --container-arg platform=linux/amd64 --container-arg arch=amd64 --container-arg all-platforms