pack should support `pack extension *` commands

[natalieparellano]

pack extension --help should show (analogously to pack buildpack --help):

  inspect     Show information about an extension
  package     Package an extension in OCI format. <- made a separate issue, please see https://github.com/buildpacks/pack/issues/1489
  new         Creates basic scaffolding of an extension.
  pull        Pull an extension from a registry and store it locally
  register    Register an extension to a registry
  yank        Yank an extension from a registry

We should probably make a separate issue for each one of these commands, as they could be implemented separately.

Edit: Made a separate issue (#1489) for pack extension package.

[cmoulliard]

What is the purpose of this command ? Can you elaborate please ? @natalieparellano

[natalieparellano]

Ah - this is to provide similar functionality to what you get with pack buildpack package (for distribution purposes). It is less important than #1468 but I added it for completeness.

[natalieparellano]

Blocking on buildpacks/rfcs#173 getting approved and merged.

[oovk]

Hi @natalieparellano I'm new to this repo. Can you please guide me to appropriate code part? and a bit of explanation about the issue would be really helpful!

[natalieparellano]

@oovk it would be awesome to get your help on this! At a high level, this is about creating a pack extension package command that is analogous to pack buildpack package, except for "extensions" - a new experimental CNB component described in buildpacks/rfcs#173.

From a pack perspective, extensions are very similar to buildpacks, except they have an extension.toml (instead of a buildpack.toml). The output of pack extension package should be either a .cnb file or an OCI image, just like pack buildpack package. A good place to start might be here.

How does that sound? Let us know if you'd like this issue assigned to you!

[itsdarshankumar]

@natalieparellano can you please assign me issue #1470 or #1489 or similar to pack extension, i'm guessing they would be a good first issue for me