Add command `pack manifest create` to create a manifest list

Context

We've been working on the idea to enable multi-arch support on CNB. A mentorship project was created on LFX and this feature is part of the efforts to build the Minimal Viable Product (MVP) during the program duration.

More information can be found:

Notes
Meeting recording

Description

Currently, the samples repository contains buildpacks and meta-buildpacks examples, using an ER diagram, we can represent those buildpacks as follow:

erDiagram
    HELLO_WORLD_BP ||--o{ HELLO_UNIVERSE_MBP : contains
    HELLO_WORLD_BP{
        string plaform_os
        string plaform_arch
    }

    HELLO_MOON_BP ||--o{ HELLO_UNIVERSE_MBP : contains
    HELLO_MOON_BP{
        string plaform_os
        string plaform_arch
    }

    HELLO_WORLD_WINDOWS_BP ||--o{ HELLO_UNIVERSE_WINDOWS_MBP : contains
    HELLO_WORLD_WINDOWS_BP {
        string plaform_os
        string plaform_arch
    }

    HELLO_MOON__WINDOWS_BP ||--o{ HELLO_UNIVERSE_WINDOWS_MBP : contains
    HELLO_MOON__WINDOWS_BP{
        string plaform_os
        string plaform_arch
    }

    HELLO_UNIVERSE_MBP {
        string plaform_os
        string plaform_arch
    }
    HELLO_UNIVERSE_WINDOWS_MBP {
        string plaform_os
        string plaform_arch
    }

These buildpacks are hosted in our docker hub repository and are available for Linux and Windows OS.

The idea is to create a new command pack buildpack manifest create to create a manifest list and combine those buildpacks. An update version of our previous ER-diagram will be:

erDiagram
    HELLO_WORLD_BP ||--o{ HELLO_UNIVERSE_MBP : contains
    HELLO_WORLD_BP{
        string plaform_os
        string plaform_arch
    }

    HELLO_MOON_BP ||--o{ HELLO_UNIVERSE_MBP : contains
    HELLO_MOON_BP{
        string plaform_os
        string plaform_arch
    }

    HELLO_WORLD_WINDOWS_BP ||--o{ HELLO_UNIVERSE_WINDOWS_MBP : contains
    HELLO_WORLD_WINDOWS_BP {
        string plaform_os
        string plaform_arch
    }

    HELLO_MOON__WINDOWS_BP ||--o{ HELLO_UNIVERSE_WINDOWS_MBP : contains
    HELLO_MOON__WINDOWS_BP{
        string plaform_os
        string plaform_arch
    }

    HELLO_UNIVERSE_MBP {
        string plaform_os
        string plaform_arch
    }
    HELLO_UNIVERSE_WINDOWS_MBP {
        string plaform_os
        string plaform_arch
    }

    HELLO_UNIVERSE_WINDOWS_MBP ||--o{ HELLO_MULTIARCH_UNIVERSE : "contains manifest"
    HELLO_UNIVERSE_MBP ||--o{ HELLO_MULTIARCH_UNIVERSE : "contains manifest"

    HELLO_MULTIARCH_UNIVERSE {
        manifest[] manifests
        string mediaType
    }

Proposed solution

A new feature on Pack can be implemented to help our users. The feature is inspired by the similar functionality in docker or podman

pack manifest create <manifest-list> <manifest> [<manifest> ... ]
  options:
       --format   Manifest list type (oci or v2s2) to use when pushing the list (default is v2s2)
       --publish Push a manifest list to a repository

Validations:

When the publish flag is used all the manifests MUST have os/arch defined otherwise an error must be thrown
The format flag will be ignored if it is not used in conjunction with the publish flag

Example

Based on the previous ER-diagram, we want to create a cnbs/sample-package:hello-multiarch-universe that combines the Linux and the Windows version of our current buildpacks.

pack manifest create cnbs/sample-package:hello-multiarch-universe \ 
                                         cnbs/sample-package:hello-universe \ 
                                         cnbs/sample-package:hello-universe-windows

Using docker Media-Types:

By default the command will create a manifest list in the local storage using the docker media types (Version 2 schema 2 v2s2) with a content similar to:

{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 226083,
         "digest": "sha256: 87a832fd6a8d6995d336c740eb6f3da015401a6e564fcbe95ee1bf37557a8225",
         "platform": {
            "os": "linux",
           "architecture": "",
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 226083,
         "digest": "sha256:670d62fbee841d256a706801a03be9c84d37fc2cd6ef7538a7af9985c3d2ed8b",
         "platform": {
            "os": "windows",
           "architecture": ""
         }
      }   
   ]
}

Using OCI Media Types:

pack manifest create  --publish --format oci cnbs/sample-package:hello-multiarch-universe \ 
                                         cnbs/sample-package:hello-universe \ 
                                         cnbs/sample-package:hello-universe-windows

Assuming all the manifests have defined os/arch the expected output is a manifest list created in a remote registry with a content similar to:

{
   "schemaVersion": 2,
   "mediaType": "application/vnd.oci.image.index.v1+json",
   "manifests": [
      {
         "mediaType": "application/vnd.oci.image.manifest.v1+json",
         "size": 226083,
         "digest": "sha256: 87a832fd6a8d6995d336c740eb6f3da015401a6e564fcbe95ee1bf37557a8225",
         "platform": {
            "os": "linux",
           "architecture": "amd64"
         }
      },
      {
         "mediaType": "application/vnd.oci.image.manifest.v1+json",
         "size": 226083,
         "digest": "sha256:670d62fbee841d256a706801a03be9c84d37fc2cd6ef7538a7af9985c3d2ed8b",
         "platform": {
            "os": "windows",
           "architecture": "amd64"
         }
      }   
   ]
}

Describe alternatives you've considered

Additional context

[x] This feature should be documented somewhere

buildpacks / pack