Add support for 32-bit arm

[SteffenDE]

Hello everyone,

I'm currently using the arm32v7/elixir image on a balena iot project using the older 32-bit raspberry pis.
As there does not seem to be any update soon over there it'd be great if bob could also build 32-bit arm images.

Keep up the great work!

[ericmj]

It looks like we can build arm/v7 images on our arm64 machines using docker buildx without performance penalty. It would require changes to our docker builds because we do not use buildx currently. Contributions in this area would be welcome.

[Zinggi]

I'd also be very interested in this. But I'd need arm32v6 (linux/arm/v6), as I've got a Raspberry Pi Zero.
Are there plans for providing more architectures?

[ericmj]

We can provide more architectures if the functionality it requires is contributed.

[Zinggi]

I got a working elixir container from here, which works for me. But of course, having more options to choose from would be a plus. I really like that the images here follow the 'immutable' approach, so the images here would be better suited for my use case. But unfortunately I don't know much about cross compiling and infra stuff to help out here.