Cache outputs of `ng build`

[fg-j]

Describe the Enhancement

Some Node.JS buildpack users are building Angular apps. This buildpack participates in the build to run ng build to create static assets. As of angular 13, angular maintains a build cache by default. It could improve buildpack rebuild times if the buildpack saves the angular cache and restores it on rebuilds.

Possible Solution

Motivation

Speed up rebuilds of angular apps with buildpacks; take advantage of built-in caching that angular knows how to handle.