The export file can now be many files, called chunks.
By default still only one chunk is exported.
This function is required in case that the exported files shall be
imported to an elasticsearch/opensearch index. The bulk import function
of elasticsearch/opensearch is limited to 100MB. To make it possible to
import YaCy files, those must be splitted into chunks. Right now we
cannot estimate the chunk size as bytes, only as number of documents.
The user must do experiments to find out the optimum chunk max size,
like 50000 docs per chunk. Try this as first attempt.
Michael Peter Christen
c20c4b8a21