feat(manager): CNB support for Spring Boot maven plugin

[nicolasbender]

Changes

Adds support for updating Cloud Native Buildpacks in the maven plugin for Spring Boot

Context

Maven plugin for Spring Boot allows to create an OCI image from a jar or war file using Cloud Native Buildpacks. The plugin offers to provide remote docker resources for builder and run images including custom buildpacks in pom.xml. This PR includes a manager to keep these resources updated.

• Buildpacks in Spring Boot

Documentation (please check one with an [x])

• [x] I have updated the documentation, or
• [ ] No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• [ ] Code inspection only, or
• [ ] Newly added/modified unit tests, or
• [ ] No unit tests but ran on a real repository, or
• [x] Both unit tests + ran on a real repository