Add DuckDB native support

[synopse]

We already included with success MongoDB as DB backend, able to leverage the best of ORM and SQLite3, using MongoDB mainly as centralized remote data storage from several microservices: each microservice has its own in-memory and SQLite3 storage, but efficiently push its data into the main shared database, mainly for archival purpose and analytics queries.

Since DuckDB is embedded and pure C, it could be a premium new storage engine for analytics, without the need to add another layer.
It won't be "another SQL" engine in addition to SQLite3 for instance. It would be an OLAP engine to be used in conjunction to the existing OLTP engines: DuckDB targets analytical, read-mostly, columnar workloads.

See https://gist.github.com/synopse/818d1e0c3457c9a2c68aa1ab24592bd0
and https://synopse.info/forum/viewtopic.php?pid=44890#p44890

First steps could be:

• implement JSON to CSV in-memory parsing and conversion (since CSV seems the best way to feed DuckDB)
• implement mormot.db.raw.duckdb.pas unit to support the raw C DuckDB API (as .dll/.so first maybe as static later on)
• implement mormot.orm.duckdb.pas unit and mormot.db.nosql.duckdb.pas unit at the same time, to leverage our JSON and DB process