Bug 25864: Lower case fields for searching

To recreate:
 1 - Have Koha using ES5 and Elasticsearch as search engine
 2 - Enable DumpTemplateVarsIntranet and DumpSearchQueryTemplate
 3 - Do a search in authorities using 'Search entire record' (abduction if using sample db)
 4 - Note no results
 5 - View the page source and find 'search_query'
 6 - Note the uppercased fields
 7 - curl 'es:9200/koha_kohadev_authorities/data/417?pretty'
 8 - Note all fields lower-cased
 9 - Apply patch
10 - Repeat search
11 - It works!

Signed-off-by: Heather Hernandez <heather_hernandez@nps.gov>
Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 2ab6018b6e)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit ecdefe969e)

Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>

Koha/SearchEngine/Elasticsearch/QueryBuilder.pm

@@ -1170,7 +1170,7 @@ sub _search_fields {
         my @search_fields;
         while (my $search_field = $result->next) {
             push @search_fields, [
-                $search_field->name,
+                lc $search_field->name,
                 $search_field->weight ? $search_field->weight : ()
             ];
         }