Publish multi-arch image manifest for controller-manager including arm64

[nojnhuh]

Describe the current behavior
ASO's official images are currently only built for linux/amd64:

% docker manifest inspect mcr.microsoft.com/k8s/azureserviceoperator:v2.3.0
{
        "schemaVersion": 2,
        "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
        "config": {
                "mediaType": "application/vnd.docker.container.image.v1+json",
                "size": 3100,
                "digest": "sha256:c21d4b8ad4a63ed679622b1c2d7adaabb5df495db340062c1e715a256d0e6481"
        },
        "layers": [
                {
                        "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
                        "size": 83932,
                        "digest": "sha256:dd5ad9c9c29f04b41a0155c720cf5ccab28ef6d353f1fe17a06c579c70054f0a"
                },
                ...
        ]
}

Compared to:

% docker manifest inspect registry.k8s.io/cluster-api-azure/cluster-api-azure-controller:v1.11.0
{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 2403,
         "digest": "sha256:c270d77a0cd5b9b3e59037b5915f3b68ef9658df7983908516f8182a8dc4c81c",
         "platform": {
            "architecture": "amd64",
            "os": "linux"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 2403,
         "digest": "sha256:3ef1aedb72804e5391c0cc7ceb5c36c2b56cbe8cef060c377b55d7fbaea038a9",
         "platform": {
            "architecture": "arm64",
            "os": "linux",
            "variant": "v8"
         }
      },
      ...
   ]
}

Describe the improvement
ASO should also build a linux/arm64 image and publish a multi-arch manifest referenced by the Helm chart and YAML manifests.

Additional context
Add any other context about the suggested improvement.

[matthchr]

Thanks for calling this to our attention!