Bug 22592: Add index scan emulation to Elasticsearch

Bug 22592: Add index scan emulation to Elasticsearch

Adds support for using the "scan indexes" action in advanced search by using faceting with a prefix filter. Requires that the field be set as facetable for anything to be found.

Test plan:
1. Apply patch
2. Go to advanced search and click "More options"
3. Select author as the search field, enter a last name and check "Scan indexes"
4. Perform search and observe the result list resembling scan results

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>