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 <Formats/NativeReader.h>
#include <Formats/NativeWriter.h>
#include <DataTypes/DataTypeFactory.h>
#include <Interpreters/Context.h>
#include <Parsers/ASTLiteral.h>
#include <Storages/StorageFactory.h>
#include <Storages/StorageStripeLog.h>
#include "StorageLogSettings.h"
#include <Processors/ISource.h>
#include <Processors/Sources/NullSource.h>
#include <Processors/Sinks/SinkToStorage.h>
#include <QueryPipeline/Pipe.h>
#include <Backups/BackupEntriesCollector.h>
#include <Backups/BackupEntryFromAppendOnlyFile.h>
#include <Backups/BackupEntryFromSmallFile.h>
#include <Backups/IBackup.h>
#include <Backups/RestorerFromBackup.h>
#include <Disks/TemporaryFileOnDisk.h>
#include <base/insertAtEnd.h>
#include <cassert>
namespace DB
{
namespace ErrorCodes
{
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
    extern const int INCORRECT_FILE_NAME;
    extern const int TIMEOUT_EXCEEDED;
    extern const int CANNOT_RESTORE_TABLE;
}
class StripeLogSource final : public ISource