feat(graphite): make sortByName optional

fixes #3360
closes #3361

public/app/plugins/datasource/graphite/gfunc.js

@@ -280,7 +280,7 @@ function (_, $) {
   addFuncDef({
     name: 'sortByName',
     category: categories.Special,
-    params: [{ name: "natural", type: "select", options: ["true", "false"] }],
+    params: [{ name: "natural", type: "select", options: ["true", "false"], optional: true }],
     defaultParams: ["false"]
   });