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 <Parsers/parseQuery.h>
#include <Parsers/ASTInsertQuery.h>
#include <Parsers/ASTDropQuery.h>
#include <Parsers/ASTFunction.h>
#include <Parsers/ASTOptimizeQuery.h>
#include <Parsers/ASTPartition.h>
#include <Parsers/ASTLiteral.h>
#include <Parsers/ASTSelectWithUnionQuery.h>
#include <Parsers/queryToString.h>
#include <Parsers/ASTCheckQuery.h>
#include <Parsers/ExpressionListParsers.h>
#include <Processors/QueryPlan/QueryPlan.h>
#include <Processors/Sources/RemoteSource.h>
#include <Processors/QueryPlan/BuildQueryPipelineSettings.h>
#include <Processors/QueryPlan/Optimizations/QueryPlanOptimizationSettings.h>
#include <Processors/QueryPlan/ReadFromPreparedSource.h>
#include <Processors/Sinks/EmptySink.h>
#include <IO/ReadBufferFromString.h>
#include <IO/Operators.h>
#include <IO/ConnectionTimeouts.h>
#include <IO/ConnectionTimeoutsContext.h>
#include <Disks/createVolume.h>
#include <Interpreters/InterpreterAlterQuery.h>
#include <Interpreters/PartLog.h>
#include <Interpreters/Context.h>
#include <Interpreters/DDLTask.h>
#include <Interpreters/InterserverCredentials.h>
#include <Interpreters/SelectQueryOptions.h>
#include <Interpreters/InterpreterSelectQuery.h>
#include <Interpreters/JoinedTables.h>