Improve Elasticsearch indexing throughput by optimizing bulk payload

For now the bulk indexing command send to ES can be limited by a number of documents (elasticsearch.reindex.bucketWriteSize).
But the optimal payload in size is 5-15M.

The bulk command should be send once:

• a number of documents is reached elasticsearch.reindex.bucketWriteSize
• or a bulk size threshold is reached elasticsearch.index.bulkMaxSize

This will prevent to send too big indexing bulk command that overwhelm ES.

Other improvements (not covered in this ticket) could be:

• send bulk command if the time to build the bulk command is longer than a timeout, to prevent long running transaction
• reschedule a new job after this timeout to prevent blocking the indexing chain.

This requires a concrete case where ES indexing is a bottleneck before impl these last improvements.