tooling: Allow alternatives to docker

[cfrantz]

Some environments do not permit docker or require exceptions to organization policies to use docker. Allow use of docker-compatible alternatives such as podman via the DOCKER environment variable.

[clundin25]

@cfrantz do you expect more tools to need this pattern?

Alternatively I would say the code should prefer podman and fallback to docker

[cfrantz]

@cfrantz do you expect more tools to need this pattern?

Alternatively I would say the code should prefer podman and fallback to docker

I don't know enough about this codebase yet to know. Of the tools listed in fpga/utils.rs, it seems like docker is the only one that has a compatible alternative like podman. My motivation for submitting this change is to solve the problem I'm experiencing in my environment.

I'm happy to generalize this solution (indeed, I tried to write something that would be generalizable), but I'd need some input from folks with more familiarity with the codebase than I to know where to land this solution.

[clundin25]

@cfrantz I think we can just make podman the default and fallback to docker. This approach is more flexible but I think we can be more opinionated in the tool.