MediaWiki ETL limit loading batch into 1!

[amindadgar]

In llama-index pipeline when trying to load documents into vectorstore, it first loads into docstore and then into vectorstore.
In any case problems raised while loading into docstore the data would be missed to be loaded into vectorstore. So we need to limit the batch size to 1 meaning the data will be 1 by 1 loaded into docstore + vectorstore.