The sqlx crate offers macros like sqlx::query_as! to validate
the query at build time and infer from the table column the return type.
If it's convenient, it requires a PostgreSQL view (or table) fantoir
to exists when building fantoir-datasource. This is a chichen egg issue,
as the tool is intended to prepare the schema too with -c flags.
This change switches from sqlx::query_as! to sqlx_query_as
and sqlx_query_scalar, without his requirement.
Note we lost the validation against SQL schema by the sqlx macros
as a trade-off.