Stablize instrumentation.js (#68853)
### What
- After adding a new API `onRequestError()` and a few fixes on `register()` for `instrumentation.js`, it's time to promote it as stable API.
- Add warning `"experimental.instrumentationHook is no longer needed to be configured in Next.js"` when you configure a `instrumentationHook` option in next.config.js
Related PRs
#67539, #67671, #67703, #67848, #67859, #67856, #67805, #68616, #68672, #68764, #68845 #68976, #68983
Closes NDX-89
