oracle writeMode 插入更新

有无支持oracle writeMode的计划，oracle使用MERGE INTO能支持有就更新没有就插入
MERGE INTO .. USING (..) ON (..)
WHEN MATCHED THEN UPDATE SET (..)
WHEN NOT MATCHED THEN INSERT (..)
VALUES (..)

Start by reviewing DataX's existing Oracle writeMode behavior and how writer options are represented. Compare the requested Oracle MERGE INTO flow for matched and unmatched rows with the current capabilities. Done means the supported behavior and scope are defined, with coverage for both update and insert paths if implementation proceeds.

Written by the indexing model from the issue text.