ref(with-sentry example): Explicitly set hideSourceMaps (#40079)

This adds a default value for `hideSourceMaps` to the `next.config.js` the `with-sentry` example app provides, so that new users will use `hidden-source-map` as their Webpack `devtool` by default in client-side builds. (This prevents browser devtools from seeing sourcemaps and therefore prevents original source code from showing up automatically in the `Sources` tab. (More information on `devtool` values can be found [here](https://webpack.js.org/configuration/devtool/).)

In conjunction with getsentry/sentry-javascript#5649, getsentry/sentry-wizard#188, and getsentry/sentry-docs#5464, this is the first step in addressing the concerns raised in getsentry/sentry-javascript#4489. See [here](getsentry/sentry-javascript#4489 (comment)) for more details.

examples/with-sentry/next.config.js

@@ -7,6 +7,16 @@ const { withSentryConfig } = require('@sentry/nextjs')
 
 const moduleExports = {
   // Your existing module.exports
+
+  sentry: {
+    // Use `hidden-source-map` rather than `source-map` as the Webpack `devtool`
+    // for client-side builds. (This will be the default starting in
+    // `@sentry/nextjs` version 8.0.0.) See
+    // https://webpack.js.org/configuration/devtool/ and
+    // https://docs.sentry.io/platforms/javascript/guides/nextjs/manual-setup/#use-hidden-source-map
+    // for more information.
+    hideSourceMaps: true,
+  },
 }
 
 // Make sure adding Sentry options is the last code to run before exporting, to