Acceptance:
- Batch size for other batches in the class should remain the same
- Batch size should be configurable via a config option which is simply a fixed number
- Default batch size for this config option should remain the same, so (100*5 = 500), so 500 (currently calculated at https://github.com/wikimedia/mediawiki-extensions-Wikibase/blob/54d283c322062e7e9ed49a6a15738bbe75d4ee10/client/includes/Usage/Sql/EntityUsageTable.php#L176-L179)
- INSERT_BATCH_SIZE_FACTOR will no longer exist.