feat: enable multi-arch builds with ARM compatibility

[rhdedgar]

What does this PR do?

Enables lllama-stack multi-architecture builds for ARM. The result is an image index, that will point to the image associated with the calling user's architecture.

On Kubernetes for example, with these changes, images are still referred to in the same manner, but will resolve to the architecture that is relevant to the node where it is to be run.

                                              --> quay.io/<user>/distribution-starter/<version>-linux-arm64
quay.io/<user>/distribution-starter/<version>-|
                                              --> quay.io/<user>/distribution-starter/<version>-linux-amd64

In practice, referring to the usual docker.io/llamastack/distribution-starter:latest should resolve to the image with the requesting user's relevant architecture, without any additional configuration on the user's side.

Closes #406

Test Plan

Tested container builds on an amd64 architecture host, and deployed the starter distribution image via llama-stack-k8s-operator to an arm64 architecture OpenShift cluster. The deployment ran and the operator's e2e test suite completed as expected.

Arm64-specific build tests run and pass on GitHub.

[ashwinb]

Thanks for doing this! ❤️

[ashwinb]

looks good to me. @leseb @cdoern you want to have one look?

[leseb]

This looks good thanks! I believe the next step is to publish a build and take inspiration from .github/workflows/build-distributions.yml in the ops repo.

[leseb]

The build never ran. https://github.com/llamastack/llama-stack/actions/runs/20277364473 there is an issue with the matrix.

[rhdedgar]

Good catch, I see the issue now. I've updated this PR with a new commit. The tests have passed again, and the build now completes: https://github.com/llamastack/llama-stack/actions/runs/20313646963.

[rhdedgar]

Might need a maintainer to remove that requested change label unless we should wait until everyone is back after New Year's before merging.