docs: update docusaurus to v3 (#5625)

* update dependencies

* update onboarding mdx

* fixes for mdx issues

* fixes for mdx compatibility

* resolve mdx errors

* fixes in reference

* fix check errors

* revert change in vale action

* fix node version in action

* fix summary in markdown

www/apps/docs/content/user-guide.mdx

@@ -35,7 +35,7 @@ The sidebar menu includes the main navigation of your Medusa admin. You can use
 
 You’ll find at the top of the page a search bar. You can use this search bar to search orders, products, customers, and more information available in your Medusa Admin.
 
-:::info Handy Shortcut
+:::info
 
 You can open the search window using the shortcuts: