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/deployments/server/deploying-on-railway.md

@@ -22,8 +22,8 @@ If you're deploying the admin plugin along with the backend, you'll need at leas
 If you also don't have a Medusa project, you can deploy to Railway instantly with this button:
 
 <a 
-  href="https://railway.app/template/zC7eOq?referralCode=TW4Qi0" class="img-url no-zoom-img">
-  <img src="https://railway.app/button.svg" alt="Deploy with Railway" class="no-zoom-img"/>
+  href="https://railway.app/template/zC7eOq?referralCode=TW4Qi0" className="img-url no-zoom-img">
+  <img src="https://railway.app/button.svg" alt="Deploy with Railway" className="no-zoom-img"/>
 </a>
 
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