chore: reorganize docs apps (#7228)

* reorganize docs apps

* add README

* fix directory

* add condition for old docs

www/apps/resources/app/troubleshooting/errors-after-upgrading/page.mdx

@@ -0,0 +1,17 @@
+export const metadata = {
+  title: `Errors After Upgrading`,
+}
+
+# {metadata.title}
+
+{/* TODO add link [Upgrade Guides](../upgrade-guides/page.mdx) */}
+
+If you run into errors after updating Medusa and its dependencies, it's highly recommended to check the Upgrade Guides if there is a specific guide for your version. These guides include steps required to perform after upgrading Medusa.
+
+If there's no upgrade guide for your version, make sure that you ran the `migrations` command in the root directory of your Medusa backend:
+
+```bash
+npx medusa migrations run
+```
+
+This ensures your backend has the latest database structure required. Then, try running your Medusa backend again and check whether the same error occurs.