[ICU-15403] Trim whitespace on storage buckets and host sets json attrs serializers (#2636)

* trim whitespace on json attrs in storage bucket serializer

* add test for storage bucket serializer

* move trimWhitespace check to application level

* add trimWhitespace to preferred_endpoints attr

* add conditional for string arr

* trim whitespace on str arr

* add check for null val

* refactor, move logic

* relocate comment

* add unit test for application serializer

addons/api/addon/generated/models/host-set.js

@@ -88,6 +88,7 @@ export default class GeneratedHostSetModel extends BaseModel {
       name: ['aws', 'azure', 'gcp'],
     },
     emptyArrayIfMissing: true,
+    trimWhitespace: true,
   })
   preferred_endpoints;