Update generator config to specify samples used in doc in nested product directories

When multiple libraries exist in a directory the generator chooses which samples to inject into the .dox files. It would be nice if we could choose which samples are used.

Start by tracing the generator configuration and how it selects samples for .dox files in nested product directories. The work is done when the configuration can explicitly choose which samples are injected when multiple libraries share a directory.

索引モデルが issue の本文から書いたものです。