[docker] Add docker images for linux/aarch64 platform

[krfricke]

Description

#31522 added ARM64 wheel builds to CI. However, as discussed in the PR and in #28103, ideally users can use rayproject/ray images directly.

We should thus add a docker image build step to CI that builds the linux/aarch64 docker images.

The main open question (at least for me) is how we make sure the platform-specific images are kept in sync and added to the potentially existing images from other platforms. Concretely:

• rayproject/ray:commithash for linux/x86_64 and linux/aarch64 should be the same
• Do we allow rayproject/ray:nightly for linux/x86_64 and linux/aarch64 to point to different commits?
• Does uploading an aarch64 image to dockerhub "add to" or replace an existing x86_64 image?

Use case

No response

[KastanDay]

For others searching about this issue, my error was

Error response from daemon: image with reference my-ray-image:latest was found but does not match the specified platform: wanted linux/arm64, actual: linux/amd64

Thank you for your efforts.

[krfricke]

We've just merged the build job for arm64 docker images with a tag suffix: #31537

This means you can now use e.g. rayproject/ray:nightly-aarch64 on arm machines.

We haven't released images for Ray 2.2.0 - first release with Docker images will be Ray 2.3.0 (targeted for mid february)

See here for all available arm64 images: https://hub.docker.com/r/rayproject/ray/tags?page=1&name=aarch64

And here for a roadmap RFC for our arm64 docker images: #31966