Management API supports sorting distributionset by "createdAt" and "lastModifiedAt" #687 (#715)

Signed-off-by: Jeroen Laverman <jeroen.laverman@bosch-si.com>

hawkbit-core/src/main/java/org/eclipse/hawkbit/repository/DistributionSetFields.java

@@ -25,6 +25,14 @@ public enum DistributionSetFields implements FieldNameProvider {
      * The description field.
      */
     DESCRIPTION("description"),
+    /**
+     * The createdAt field.
+     */
+    CREATEDAT("createdAt"),
+    /**
+     * The lastModifiedAt field.
+     */
+    LASTMODIFIEDAT("lastModifiedAt"),
     /**
      * The version field.
      */