Consider storage format for all reference tables

[paulseamer]

Consider whether 4 & 5 would be better (easier to read/edit/ingest) stored in an alternative format.

1. assumpions_register - CSV ✅
2. classification_traceability_matrix - YAML ✅
3. fun_area_catalog - CSV❓
4. classification_register - MD table ❓
5. conversion_archetypes_catalog - MD table ❓

[yiwen-h]

enjoyed the usage of YAML 🍠 for the classification traceability matrix

MD table is probably least usable in my opinion so whatever we can do to avoid those is appreciated