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. 

try
        {
            if (zookeeper_name == default_zookeeper_name)
            {
                current_zookeeper = getContext()->getZooKeeper();
            }
            else
            {
                current_zookeeper = getContext()->getAuxiliaryZooKeeper(zookeeper_name);
            }
        }
        catch (...)
        {
            if (!attach)
                dropIfEmpty();
            throw;
        }
    }
    bool skip_sanity_checks = false;
    
    if (attach)
    {
        if (current_zookeeper && current_zookeeper->exists(replica_path + "/flags/force_restore_data"))
        {