Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

#include <filesystem>
#include <Core/Settings.h>
#include <Databases/DatabaseOnDisk.h>
#include <Databases/DatabaseOrdinary.h>
#include <Databases/DatabasesCommon.h>
#include <Databases/DDLDependencyVisitor.h>