Fix local links from docs to Storybook (#624)

* Redirect Storybook link from docs site to Storybook dev server

* Add safeguard to avoid redirects in prod environments

Theoretically you should only hit this page in dev environments because
primer.style's reverse proxy redirects this directory to the SB instance,
but when that configuration changes we don't want to expose this local
redirect.

apps/docs/src/pages/brand/storybook.tsx

@@ -0,0 +1,18 @@
+/**
+ * This page is only used during local development to redirect Storybook links to the Storybook dev server
+ * On production this directory is redirected to the privately hosted Storybook by primer.style
+ */
+
+import {useEffect} from 'react'
+
+const StorybookRedirect = ({location}) => {
+  useEffect(() => {
+    if (process.env.NODE_ENV === 'development') {
+      window.location.replace(`http://localhost:6006${location.search}`)
+    }
+  }, [])
+
+  return null
+}
+
+export default StorybookRedirect