Deduplication as lookup - if doc_schema not specified, then lookups will fail..

[Alex-Ikanow]

.. because the doc service won't be pulled into the list of JARs deployed with the app

Adding an override field so for the lookup case you can just set it to search_index_service .. of course this can still fail since you might not have the right data service enabled, but it makes it a bit safer and more transparent