Add global font and styles to the root layout

### Context
Resources: [Next.js: Font Module](https://nextjs.org/docs/pages/api-reference/components/font), [Next.js: Global Style](https://nextjs.org/learn/dashboard-app/css-styling#global-styles)

In the page router, we added the `link` tag to the `_document` file for Google font (the global font) and the global styles to the `_app` file.

In the app router, we'll add them to the root layout and load Google font using the Next.js font module.

### Problem or idea
As stated above, add the global font and styles to the root layout.

### Solution or next step
Add the following items to the root layout:
- Google font using the font module
- Global styles