Publish static images as manifest lists.

[mattmoor]

A sample run of this (on my project) produced:

    crane manifest gcr.io/mattmoor-knative/static:nonroot
    {
       "schemaVersion": 2,
       "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
       "manifests": [
          {
             "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
             "size": 526,
             "digest": "sha256:2b4a48f7c192111b0ff59633f1ac68f0079b8e8306bf0c5cb55169241ba464c9",
             "platform": {
                "architecture": "amd64",
                "os": "linux"
             }
          },
          {
             "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
             "size": 526,
             "digest": "sha256:9169d04187d456913f000daeddc3fa2c2ae2e27dca5297b697d5c1d6f5b132c7",
             "platform": {
                "architecture": "arm64",
                "os": "linux"
             }
          }
       ]
    }

Based on: #586
Fixes: #583

[mattmoor]

I see arm64 images under https://gcr.io/distroless/static 🤩

[mattmoor]

Ok, I redeployed https://pizzaplanetv1-test-image.default.mattmoor.io changing just .ko.yaml to include :nonroot-arm64 and it works 🤩

[dekkagaijin]

Thanks for dragging distroless kicking and screaming into its archful future

[morlay]

Can't wait to use this to add distroless arm64 build of istio https://github.com/querycap/istio

blocking by gcr.io/distroless/static-debian10 and gcr.io/distroless/cc 😭

[mattmoor]

@morlay those should be pretty easy to add next, I'm starting small 😉

[morlay]

@mattmoor Cool. i see the codebase is upgraded. Waiting those images to land on gcr.io