Support bulk imports in import_without_validations_or_callbacks

[colinmroberts]

When dealing with bulk imports for DB Backend records, we should add better support for refreshing records from the DB. Specifically, in import_without_validations_or_callbacks in kafka_source.rb, we currently do a single DB query for each record that is being imported. When there is a bulk import, especially with thousands of records, this is extremely slow.

If we could bulk-query the list of IDs and match them up with the records being imported, this would make this import much more efficient