Add arm64 images

[timower]

When developing on an apple silicon mac, docker uses linux/arm64 by default.
Using the amd64 image is possible, but is a lot slower.

It'd be nice if the CI also publishes arm64 images. Locally the Dockerfiles do seems to work for arm64 (at least v2.x).

[Eeems]

I'd be happy to accept a PR to add this to 3.x (and 4.x when it's done). I don't think any of us will get to it for a while otherwise.