Fix "Export Everything" to properly constrain types (elastic#21402)

This fixes the "Export Everything" button on the Saved Objects Management screen so that the export properly constrains the saved object types returned.

Previously, this endpoint was incorrectly returning objects that were not requested (such as the `config` object). This behavior is exacerbated with [Spaces](elastic#18948) because the export button would incorrectly export the Space objects, which in turn do not make sense to import.

src/core_plugins/kibana/server/routes/api/management/saved_objects/scroll.js

@@ -49,7 +49,7 @@ export function registerScrollForExportRoute(server) {
       const savedObjectsClient = req.getSavedObjectsClient();
       const objects = await findAll(savedObjectsClient, {
         perPage: 1000,
-        typesToInclude: req.payload.typesToInclude
+        type: req.payload.typesToInclude
       });
       const response = objects.map(hit => {
         const type = hit.type;