Add support for Cloud Native Buildpack extensions when building images.
Depends on #41352
Comment From: wilkinsona
See https://github.com/spring-projects/spring-boot/issues/42590#issue-2579203360 for an example of why this would be useful.
Comment From: pr11me
Here's another use case: building the image in CI without internet access, e.g. due to corporate proxy or air-gapped scenario.
The problem here is that the builder tries to download a JRE/JDK from somewhere during the build process.
Using extensions, one could extend the run image with a JRE and avoid the download.