private File outputFile() {
        var a = project.getArtifact();
        var name = project.getArtifactId() + "-" + a.getVersion() + "-shaded." + a.getArtifactHandler().getExtension();
        return new File(outputDirectory, name);
    }
Wrapper around maven-shade-plugin's {@link DefaultShader} for packaging Vespa fat jars for `$VESPA_HOME/lib/jars`.
The produced fat jar will add dependencies which are already installed in lib/jars to manifest's "Class-Path" instead of embedding.

@author bjorncs
bundle-plugin/src/main/java/com/yahoo/container/plugin/mojo/AssembleFatJarMojo.java