WIP: Publish App layers metadata

[mike-sul]

Extend the publish tool to include app layers metadata into the app manifest.

[mike-sul]

@doanac This goes together with foundriesio/ci-scripts#285

As a result the app manifest looks like:

{
   "annotations": {
      "compose-app": "v1"
   },
   "config": {
      "digest": "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
      "mediaType": "application/vnd.oci.image.config.v1+json"
   },
   "layers": [
      {
         "digest": "sha256:1ac07762dcf1149eacd23ee64f64442ca26769033edc76284d3194837422a901",
         "mediaType": "application/octet-stream",
         "size": 587
      },
      {
         "annotations": {
            "layers-meta": "v1"
         },
         "digest": "sha256:3ef0d2568749c8b926928f403688d8dc30efd41bc68fa24718394cf59fa3e8b7",
         "mediaType": "application/octet-stream",
         "size": 3734
      }
   ],
   "manifests": [
      {
         "mediaType": "application/vnd.oci.image.index.v1+json",
         "size": 1629,
         "digest": "sha256:a4e3b4f5be9a91bf75236a7115331faf52d918dbdc94b0bfd2b44a3afa0efae8",
         "platform": {
            "architecture": "amd64",
            "os": ""
         }
      },
      {
         "mediaType": "application/vnd.oci.image.index.v1+json",
         "size": 1787,
         "digest": "sha256:cb5c4ffa7afec43bba8fc192896280076c246a35646fb96ebda798f12c046eb7",
         "platform": {
            "architecture": "arm",
            "os": ""
         }
      },
      {
         "mediaType": "application/vnd.oci.image.index.v1+json",
         "size": 1789,
         "digest": "sha256:709c840b5777f63d809fb87671236a29c410c92198eaa9a5972d264ccd5938d8",
         "platform": {
            "architecture": "arm64",
            "os": ""
         }
      }
   ],
   "mediaType": "application/vnd.oci.image.manifest.v1+json",
   "schemaVersion": 2
}

The layers meta layer/json looks like:

{
  "amd64": {
    "fs_block_size": 4096,
    "layers": {
      "sha256:388169b3a3d311d29d28eeba4fa687b0c18207b040f74b49622e5eca4b765fa6": {
        "size": 0,
        "usage": 28928,
        "archive_size": 120
      },
      ...
    }
  },
  "arm": {
    "fs_block_size": 4096,
    "layers": {
      "sha256:4271bf13258b585def40291fcb3b0490ce089b76fe80a5f1aa672e925ec81bcb": {
        "size": 127,
        "usage": 28962,
        "archive_size": 175
      },
    ...
  },
  "arm64": {
    "fs_block_size": 4096,
    "layers": {
      "sha256:06ade89b14b08b385b7add0a1c420a11d7840018ef39e96da50912076a94b580": {
        "size": 6030081,
        "usage": 7751054,
        "archive_size": 1811031
      },
      ...
  }
}