WIP: Quarkus test support

[vaslabs]

Still figuring things about but creating a draft if anyone's interested to peek into the future of #6771

Current issues:

• For some reason quarkus-junit does not make it into the serialized app model (although it is present in quarkusDependencies and the AppModel case class. Perhaps because it's a duplicate?)
• The above is probably causing the classpath issue of

136] Caused by: java.lang.ClassNotFoundException: io.quarkus.test.junit.TestBuildChainFunction
136]    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
136]    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
136]    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)