docs: add build worker optout error back with upgrade advice (#60826)

x-ref: https://github.com/vercel/next.js/pull/60820/files#r1457566492

Closes NEXT-2151

errors/webpack-build-worker-opt-out.mdx

@@ -0,0 +1,19 @@
+---
+title: Webpack Build Worker automatic opt-out
+---
+
+## Webpack Build Worker Opt-out
+
+#### Why This Error Occurred
+
+The Next.js config contains custom webpack configuration, as a result, the webpack build worker optimization was disabled.
+
+The webpack build worker optimization helps alleviate memory stress during builds and reduce out-of-memory errors although some custom configurations may not be compatible.
+
+#### Possible Ways to Fix It
+
+Upgrade Next.js to latest (>= 14.1.0) to remove this warning.
+
+```
+npm i next@latest
+```