Allow build image caches to use the container file system instead of volumes

[scottfrederick]

When the Maven spring-boot:build-image goal or Gradle bootBuildImage task invokes the CNB lifecycle API, it creates and mounts volumes for the lifecycle to use as build and launch caches. Some restrictive environments like BitBucket don't allow writing to these volumes, but do allow writing to a specific location on the build container file system. The plugins should be enhanced to allow a user to configure file system locations for the build and launch caches instead of volumes.

See https://github.com/spring-projects/spring-boot/issues/25606 for an example of an issue related to this, and the Pack cache options RFC for the pack CLI implementation of a similar capability.

[mimozell]

Are there any plans around this? It's been a while :D

[scottfrederick]

@mimozell There are no immediate plans to implement this. We haven't seen enough demand for the feature to make it a high priority relative to other things the team is working on. Contributions are always welcomed.