Related Families metadata

@bequinha151 has developed with Gemini a large JSON file that contains a graph structure for families that are related, both 'superfamilies' (e.g. Merriweather + Merriweather Sans) and 'sibling families' (e.g. [Cossette Titre](https://fonts.google.com/specimen/Cossette+Titre) + [Cossette Texte](https://fonts.google.com/specimen/Cossette+Texte), which are pretty much CSS families that ought to be merged into a single VF design space but for lack of app support (especially Google Workspace editors) they remain separate families)

I stuck the data file here, and I'm asking @m4rc1e to take a look at it and make some way to QA the data and maintain it over time.

https://github.com/google/fonts/tree/rebecca-related-familes-json

Start with the linked rebecca-related-familes-json directory and inspect the large JSON graph for superfamily and sibling-family relationships. Determine how the data can be QAed and maintained over time; done means the relationship data has a repeatable validation and maintenance approach.

Written by the indexing model from the issue text.