Add history metadata to layers created by pack builder create

[edmorley]

Description

Currently builder images created using pack builder create have blank descriptions for each layer when the builder is inspected using docker history <builder_image_name>.

This also causes the Docker Hub web layer UI to be blank:
https://hub.docker.com/layers/heroku/builder/22/images/sha256-72a0f9629ffb8826afed1ec47991cf9802b640ad44afdda6fbc4a14037cc4e4b?context=repo

Compare this to the docker history shown for an app image created by pack build, which includes descriptions for each layer - thanks to buildpacks/lifecycle#1099 and buildpacks/imgutil#202.

Proposed solution

To add history metadata for each layer in the builder image.

For example, each buildpack layer would be named after the buildpack ID and version.

For ideas on naming/style, see the descriptions used for the app image here:
https://github.com/buildpacks/lifecycle/blob/751c7a2737be2e6a8f66bfcc2e0cf0058661d6ff/acceptance/exporter_test.go#L104-L109

[edmorley]

Example of how this currently shows up on Docker Hub: