[release-1.2] 🐛 Fix Architecture metadata in Dockerfiles for distroless base image references

[chrischdi]

Manual cherry-pick of #7070

What this PR does / why we need it:

References the correct architecture for the distroless base image. Before this commit, docker would have chosen the platform of the docker host.

Current main:

$ uname -m
arm64
$ ARCH=ppc64le REGISTRY=test make docker-build-core
$ docker inspect docker.io/test/cluster-api-controller-ppc64le:dev | grep Architecture
        "Architecture": "arm64",

WIth this commit:

$ uname -m
arm64
$ ARCH=ppc64le REGISTRY=test make docker-build-core
$ docker inspect docker.io/test/cluster-api-controller-ppc64le:dev | grep Architecture
        "Architecture": "ppc64le",

Note: I had to move the ARG ARCH above the first FROM, otherwise it is not set/empty in FROM lines.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

[k8s-ci-robot]

@chrischdi: This issue is currently awaiting triage.

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[killianmuldoon]

/lgtm

[sbueringer]

/lgtm
/approve

[k8s-ci-robot]

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