Dockerfile: build arm64 variants

[akerouanton]

• Closes Multi-arch container image #262

Make it possible to build both amd64 and arm64 Docker images. This can be done with:

docker build --platform linux/amd64,linux/arm64 --tag pwru  .

GHA release workflow only handles GH release artifacts, so the out-of-tree CI job or manual process used to publish images on Docker Hub will have to be updated accordingly.

Also, fix the release script used during image build to support cross-compilation of amd64 on arm64 machines.

(Note that a standalone Docker Engine has to be configured with the containerd snapshotter enabled to build multi-arch images. See https://docs.docker.com/engine/storage/containerd/)

[jschwinger233]

Thank you!

@brb You know this better than me, how do you like it?

[brb]

Thanks!

[brb]

@akerouanton I was informed by @aanm that Docker Hub, where we publish cilium/pwru images, does not support the multi-arch.

[akerouanton]

Docker Hub [...] does not support the multi-arch.

What do you mean @aanm? Docker Hub itself does support multi-arch images. For instance: https://hub.docker.com/r/albinkerouanton006/pwru/tags.

[aanm]

@brb @akerouanton what I meant was that hub.docker.com does not build multi-arch images but it's fine to publish.

[akerouanton]

@aanm I see. I think a build hook could do the job, but Cilium needs to have either a Docker Pro, Team, or Business subscription as is noted at the top of that doc page. Is that the case?

[aanm]

@aanm I see. I think a build hook could do the job, but Cilium needs to have either a Docker Pro, Team, or Business subscription as is noted at the top of that doc page. Is that the case?

@akerouanton no, that's not the case. All multi-arch builds that Cilium has are done via GitHub actions. For example here