Add jandex index to all artifacts

[mvysny]

Vaadin 14.4.6: in order to support Quarkus, so-called Jandex index needs to be created. The reason is that Quarkus doesn't rely on classpath scanning to discover classes; instead it uses Jandex index. Alternatively, the jar files needs to have an empty beans.xml file present. Please see https://quarkus.io/guides/cdi-reference for more details.

These files need to be present in all jar files containing any classes that are discovered by classpath scanning, for example @NpmPackage-annotated classes etc.