[Ingestor] Clean up products without product files

[tangobravo62]

Products without product files (pure product metadata) are kept around for statistics reasons. However, over time this leads to an accumulation of hundreds of thousands or even millions of "empty product shells".

A cleanup mechanism, which is balanced with the requirements of production monitoring, needs to be designed and implemented. Since there is already a product file cleanup mechanism in the Ingestor, this component is the most obvious candidate for such a functionality.