docs(configuration): add allowedHosts: 'auto' (#5343)

Author: snitin315

src/content/configuration/dev-server.mdx

@@ -146,6 +146,25 @@ Usage via the CLI:
 npx webpack serve --allowed-hosts all
 ```
 
+When set to `'auto'` this option always allows `localhost`, [`host`](#devserverhost), and [`client.webSocketURL.hostname`](#websocketurl):
+
+**webpack.config.js**
+
+```javascript
+module.exports = {
+  //...
+  devServer: {
+    allowedHosts: 'auto',
+  },
+};
+```
+
+Usage via the CLI:
+
+```bash
+npx webpack serve --allowed-hosts auto
+```
+
 ## `devServer.bonjour`
 
 `boolean` `object`