Add support for "buildpacks" field in app.json

[ahmetb]

No description provided.

[ahmetb]

@jamesward I feel like we should just assume --builder=heroku/buildpacks, and then have an optional array for --buildpack, so we call the CLI like:

pack build --builder=heroku/buildpacks [--buildpack=foo --buildpack=bar ...]

wdyt?

[jamesward]

Sounds great to me but we do need to push to get a Cloud Run bug fixed where most buildpack built images do not currently work (Node & Python are currently broken).

[ahmetb]

Yes learned it the hard way yesterday.
The whole project does not seem stable or ready for prime-time. I won’t be touching this anytime soon.

[jamesward]

It’s actually a bug in Cloud Run, because the containers work fine in docket.

[jamesward]

There is a way to specify specific buildpacks via a project.toml file in the root:
buildpacks/pack#421