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 <Common/ThreadPool.h>
#include <Poco/DirectoryIterator.h>
#include <Parsers/ParserCreateQuery.h>
#include <Parsers/ASTCreateQuery.h>
#include <Parsers/parseQuery.h>
#include <Interpreters/InterpreterCreateQuery.h>
#include <Interpreters/Context.h>
#include <Interpreters/loadMetadata.h>
#include <Interpreters/executeQuery.h>
#include <Databases/DatabaseOrdinary.h>
#include <Databases/TablesLoader.h>
#include <IO/ReadBufferFromFile.h>
#include <IO/ReadHelpers.h>
#include <Common/escapeForFileName.h>
#include <Common/typeid_cast.h>
#include <filesystem>
#include <Common/logger_useful.h>
namespace fs = std::filesystem;
namespace DB
{
namespace ErrorCodes
{
    extern const int NOT_IMPLEMENTED;
    extern const int LOGICAL_ERROR;
}
static void executeCreateQuery(