feat: Add multi-arch support for releases.

[cwboden]

Addresses #46.

Open to changes in the approach, though I confirmed this built locally for me on WSL2.

I elected to keep the non-multi-arch build steps around for backwards compatibility, instead introducing new *-multiarch steps that are now called from the on_release Workflow.

In addition, I updated Earthfile.md and tidied it up so it'll look nicer when rendered.

[djeebus]

Thanks! It looks like you made a release-binaries-multiarch, but the existing release-binaries is already multiarch (since build-binaries, which provides the binaries, is itself multiarch). Unless I'm missing something, want to remove the release-binaries-multiarch target? Everything else looks good!

[cwboden]

@djeebus Updated! Let me know if there's anything else you'd like me to touch up. Cheers.

[mplachter]

@cwboden, it looks like this got out of date with the upstream, would love to get this in let me know when you can fix it 🙇

[cwboden]

@mplachter Done

[djeebus]

yup, looks good, thanks!