doc: update typo in instrumentation page (#52311)

There's a small typo: `[pagesExtension]` -> `[pageExtensions]`. 

Got confused why my instrumentation hook was not called. When I searched my source code for `pagesExtension` there was no occurrence so I thought I did not use it; soon after I realized the field in the docs has a typo .

docs/02-app/01-building-your-application/05-optimizing/08-open-telemetry.mdx

@@ -70,7 +70,7 @@ export function register() {
 > **Good to know**
 >
 > - The `instrumentation` file should be in the root of your project and not inside the `app` or `pages` directory. If you're using the `src` folder, then place the file inside `src` alongside `pages` and `app`.
-> - If you use the [`pagesExtension` config option](/docs/app/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
+> - If you use the [`pageExtensions` config option](/docs/app/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
 > - We have created a basic [with-opentelemetry](https://github.com/vercel/next.js/tree/canary/examples/with-opentelemetry) example that you can use.
 
 </AppOnly>
@@ -80,7 +80,7 @@ export function register() {
 > **Good to know**
 >
 > - The `instrumentation` file should be in the root of your project and not inside the `app` or `pages` directory. If you're using the `src` folder, then place the file inside `src` alongside `pages` and `app`.
-> - If you use the [`pagesExtension` config option](/docs/pages/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
+> - If you use the [`pageExtensions` config option](/docs/pages/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
 > - We have created a basic [with-opentelemetry](https://github.com/vercel/next.js/tree/canary/examples/with-opentelemetry) example that you can use.
 
 </PagesOnly>

docs/02-app/01-building-your-application/05-optimizing/09-instrumentation.mdx

@@ -13,7 +13,7 @@ If you export a function named `register` from a `instrumentation.ts` (or `.js`)
 >
 > - This feature is **experimental**. To use it, you must explicitly opt in by defining `experimental.instrumentationHook = true;` in your `next.config.js`.
 > - The `instrumentation` file should be in the root of your project and not inside the `app` or `pages` directory. If you're using the `src` folder, then place the file inside `src` alongside `pages` and `app`.
-> - If you use the [`pagesExtension` config option](/docs/app/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
+> - If you use the [`pageExtensions` config option](/docs/app/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
 > - We have created a basic [with-opentelemetry](https://github.com/vercel/next.js/tree/canary/examples/with-opentelemetry) example that you can use.
 
 </AppOnly>
@@ -24,7 +24,7 @@ If you export a function named `register` from a `instrumentation.ts` (or `.js`)
 >
 > - This feature is **experimental**. To use it, you must explicitly opt in by defining `experimental.instrumentationHook = true;` in your `next.config.js`.
 > - The `instrumentation` file should be in the root of your project and not inside the `app` or `pages` directory. If you're using the `src` folder, then place the file inside `src` alongside `pages` and `app`.
-> - If you use the [`pagesExtension` config option](/docs/pages/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
+> - If you use the [`pageExtensions` config option](/docs/pages/api-reference/next-config-js/pageExtensions) to add a suffix, you will also need to update the `instrumentation` filename to match.
 > - We have created a basic [with-opentelemetry](https://github.com/vercel/next.js/tree/canary/examples/with-opentelemetry) example that you can use.
 
 </PagesOnly>