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>
 
 ---

www/apps/docs/content/deployments/storefront/deploying-next-on-vercel.mdx

@@ -13,8 +13,8 @@ In this document, you’ll learn how to deploy the Next.js Starter Template on V
 Alternatively, you can directly deploy the Next.js Starter Template to Vercel with this button.
 
 <a 
-  href="https://vercel.com/new/clone?repository-url=https%3A%2F%2Fgithub.com%2Fmedusajs%2Fnextjs-starter-medusa.git&env=NEXT_PUBLIC_MEDUSA_BACKEND_URL&envDescription=URL%20of%20your%20Medusa%20Backend" class="img-url no-zoom-img">
-  <img src="https://vercel.com/button" alt="Deploy with Vercel" class="no-zoom-img"/>
+  href="https://vercel.com/new/clone?repository-url=https%3A%2F%2Fgithub.com%2Fmedusajs%2Fnextjs-starter-medusa.git&env=NEXT_PUBLIC_MEDUSA_BACKEND_URL&envDescription=URL%20of%20your%20Medusa%20Backend" className="img-url no-zoom-img">
+  <img src="https://vercel.com/button" alt="Deploy with Vercel" className="no-zoom-img"/>
 </a>
 
 :::note