Add spring boot exploded mode

[jbonofre]

Right now, K5 only supports repackaged spring boot application jar, wrapping all jar in uber jar. Then, K5 uses JarLauncher to launch the spring boot application.

However, this is not the running mode recommended by spring boot. K5 should support running spring boot application in exploded mode (similar to spring-boot:run maven goal).

It means that K5 needs:

• to scan @SpringBootApplication annotation to find the Main class
• to have a way (using spring boot app pom for instance) to find all dependencies to populate the classloader
• don't use JarLauncher but create classloader and run instead

This preparation step should be performed at build time (CLI/maven/gradle plugin), not at build time.