message: docs: add side effect `package.json` in app structure
  With this change we add the special `package.json` which is used to mark the application free of non-local side-effects in the application source files section
  PR Close
diff: @@ -90,6 +90,7 @@ Angular components, templates, and styles go here.
  | `app/app.component.css` | Defines the base CSS stylesheet for the root `AppComponent`. |
  | `app/app.component.spec.ts` | Defines a unit test for the root `AppComponent`. |
  | `app/app.module.ts` | Defines the root module, named `AppModule`, that tells Angular how to assemble the application. Initially declares only the `AppComponent`. As you add more components to the app, they must be declared here. |
  +| `app/package.json` | This file is generated only in applications created using `--strict` mode. This file is not used by package managers. It is used to tell the tools and bundlers whether the code under this directory is free of non-local [side-effects](https://webpack.js.org/guides/tree-shaking/#mark-the-file-as-side-effect-free). |
  ### Application configuration files
  