fix(nextjs): Update code sample in Advanced Usage of Webpack (#3677)

The advanced usage of Webpack was valid in a prior version of the SDK. This PR updates that code sample, besides removing some comments to reduce noise. If a user wants to read that noise or just learn more about it, a link to the `manual-setup` page has been included.

Author: iker-barriocanal

src/includes/configuration/sourcemaps/tools/webpack/advanced-usage/javascript.mdx

@@ -0,0 +1,11 @@
+```javascript
+module.exports = {
+  output: {
+    // Make maps auto-detectable by sentry-cli
+    filename: "[name].js",
+    sourceMapFilename: "[name].js.map",
+    // Other `output` configuration
+  },
+  // Other configuration
+};
+```

src/includes/configuration/sourcemaps/tools/webpack/advanced-usage/javascript.nextjs.mdx

@@ -0,0 +1,26 @@
+```javascript {filename:next.config.js}
+const { withSentryConfig } = require("@sentry/nextjs");
+
+const moduleExports = {
+  webpack: (config, options) => {
+    devtool = 'source-map',
+    config.output = {
+      ...config.output,
+      // Make maps auto-detectable by sentry-cli
+      filename: "[name].js",
+      sourceMapFilename: "[name].js.map",
+    };
+    return config;
+  },
+  productionBrowserSourceMaps: true,
+  // Other nextjs configuration
+};
+
+const SentryWebpackPluginOptions = {
+  // Additional config options for the Sentry Webpack plugin.
+};
+
+module.exports = withSentryConfig(moduleExports, SentryWebpackPluginOptions);
+```
+
+Learn more about the Webpack usage for the Next.js SDK in [Extend Default Webpack Usage](/platforms/javascript/guides/nextjs/manual-setup/#extend-default-webpack-usage).

src/platforms/javascript/common/sourcemaps/tools/webpack.mdx

@@ -77,16 +77,7 @@ Set up the `SentryWebpackPlugin` as the last running plugin, otherwise, the resu
 
 If you prefer to upload source maps manually, configure Webpack to output source maps:
 
-```javascript
-module.exports = {
-  output: {
-    path: path.join(__dirname, "dist"),
-    filename: "[name].js",
-    sourceMapFilename: "[name].js.map",
-  },
-  // other configuration
-};
-```
+<PlatformContent includePath="configuration/sourcemaps/tools/webpack/advanced-usage" />
 
 If you use [SourceMapDevToolPlugin](https://webpack.js.org/plugins/source-map-dev-tool-plugin) for more fine-grained control of source map generation, turn off `noSources` so Sentry can display proper source code context in event stack traces.