warn about skipped dependencies

[luxe]

Some dependencies cannot be processed by oss_audit because they lack metadata. We currently skip these dependencies which prevent them from appearing in the BOM yaml.

It would be helpful to have additional DEBUG messages that print the skipped target dependencies. This will give us an idea of what was left out of our generated BOM and what we may want to fix to get them included.

Or the rule could generate an additional output like target.bom-skipped.yaml