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. 

{
    if (database->getEngineName() != "Ordinary")
        return;
    if (context->getSettingsRef().allow_deprecated_database_ordinary)
        return;
    try
    {
        
        startupSystemTables();
        auto local_context = Context::createCopy(context);
        local_context->setSetting("check_table_dependencies", false);
        convertOrdinaryDatabaseToAtomic(local_context, database);
        auto new_database = DatabaseCatalog::instance().getDatabase(DatabaseCatalog::SYSTEM_DATABASE);