Possibility to split app-image creation and final package

[HiranChaudhuri]

JPackage, as it is called from this plugin is very suitable for doing the whole job.

If, however, the app-image needs customizatin before ultimately being packaged or the app-image shall be reused by other proces steps (e.g. creating an appimage.org style package), JPackage should be able to run in two phases.

The way to run it from command line is shown in https://stackoverflow.com/a/70774514/4222206
It could be resembled in two executions of this maven plugin.