Add multi-arch support for alpine

[mikesir87]

Now that alpine is supporting multi-arch, it'd be great to have multi-arch support for all node:alpine variants.

I'm willing to put in a PR, but from what I can tell, we only need to update the node file in the official-images here and add the other architectures. Shouldn't everything else just fall into place from there? 🤔

[tianon]

I believe that the generate-stackbrew-library.sh script here needs https://github.com/nodejs/docker-node/blob/master/architectures to be updated to include alpine in more lines.

[mikesir87]

Gotcha. Is there any good way to test the updates, other than just running it through the pipeline?

[SimenB]

Yes, should be enough to update that file.

[mikesir87]

Ok. File changed and PR submitted. 👍