docs: add updates documentation (#11146)

- Add chapter on updating Medusa
- Add section in UI docs about updating UI packages in standalone applications

Closes #10927
Closes DX-1282

www/apps/book/sidebar.mjs

@@ -553,6 +553,12 @@ export const sidebar = sidebarAttachHrefCommonOptions([
       },
     ],
   },
+  {
+    type: "link",
+    path: "/learn/update",
+    title: "Updating Medusa",
+    chapterTitle: "Updates",
+  },
   {
     type: "link",
     path: "/learn/more-resources",