Replace usage of deprecated ddev --mutagen-enabled flag

See https://github.com/ddev/ddev/blob/9c3de4966ba930045e79442299fa2a57e3f9ce4a/cmd/ddev/cmd/config.go#L247-L248, causes info: "Flag --mutagen-enabled has been deprecated, please use --performance-mode instead"

Author: Matthias Schmidt

docs/getting_started/install_with_ddev.md

@@ -92,7 +92,7 @@ Now, configure the database connection for your [[= product_name =]] project. De
 If you're using macOS or Windows, you might want to enable [Mutagen](https://ddev.readthedocs.io/en/latest/users/install/performance/#mutagen) to improve performance. You can do this by running the following command:
 
 ```bash
-ddev config --mutagen-enabled
+ddev config --performance-mode=mutagen
 ```
 
 See [DDEV performance documentation](https://ddev.readthedocs.io/en/latest/users/install/performance/) for more.