[adapters] Use an adapter for serializing entities to a bare python structure which may be used for e.g. JSON export or other and allow to have different serializations for each entity types. Closes #6378035

[pkg] 3.20.12

[dataimport] Fallback from COPY to executemany (closes #9135780) If we can't build a suitable COPY command (e.g. because data has unsupported type), use executemany instead. Regression introduced in 3.20.0.