refactor(starter): upgrade to new version of gatsby

internal/testing/__mocks__/site-metadata.ts

@@ -0,0 +1,17 @@
+import author from "./author";
+import menu from "./menu";
+
+export default {
+  site: {
+    siteMetadata: {
+      url: "https://www.lumen.local",
+      title: "Blog by John Doe",
+      subtitle:
+        "Pellentesque odio nisi, euismod in, pharetra a, ultricies in, diam. Sed arcu.",
+      copyright: "All rights reserved.",
+      postsPerPage: 4,
+      author,
+      menu,
+    },
+  },
+};