search-api: Use unmapped_type = keyword rather than long

Not entierly sure why it was set to `long` previously, but since this is
in the `defaultSort` function that is only used for `keywordField`'s i
think its safe to change it to keyword.

Author: jnatten

search-api/src/main/scala/no/ndla/searchapi/service/search/MultiDraftSearchService.scala

@@ -217,6 +217,7 @@ trait MultiDraftSearchService {
       val pagination     = getStartAtAndNumResults(settings.page, settings.pageSize).?
       val aggregations   = buildTermsAggregation(settings.aggregatePaths, indexServices.map(_.getMapping))
       val index          = getSearchIndexes(settings).?
+      val sort           = getSortDefinition(settings.sort, searchLanguage)
       val searchToExecute = search(index)
         .query(filteredSearch)
         .suggestions(suggestions(settings.query.underlying, searchLanguage, settings.fallback))
@@ -225,7 +226,7 @@ trait MultiDraftSearchService {
         .size(pagination.pageSize)
         .highlighting(highlight("*"))
         .aggs(aggregations)
-        .sortBy(getSortDefinition(settings.sort, searchLanguage))
+        .sortBy(sort)
 
       // Only add scroll param if it is first page
       val searchWithScroll =

search-api/src/main/scala/no/ndla/searchapi/service/search/SearchService.scala

@@ -297,7 +297,7 @@ trait SearchService {
           fieldSort(s"$withLanguage.$sortLanguage.raw")
             .sortOrder(order)
             .missing("_last")
-            .unmappedType("long")
+            .unmappedType("keyword")
       }
     }