Storybook example broken after webpack 5 upgrade

**Describe the bug**
The recent webpack 5 upgrade (https://github.com/expo/expo-cli/pull/3763), shipped with Expo 48, removed the `withUnimodules` method `@expo/webpack-config` and provides no alternative.
`withUnimodules` is still erroneously referenced in the `@expo/webpack-config` [README](https://github.com/expo/expo-cli/blob/main/packages/webpack-config/README.md), and is also used in the `with-storybook` [example in this repo](https://github.com/expo/examples/blob/471fb60e690fd4fd5fcf934cd9adbb635b0b5f4b/with-storybook/.storybook/webpack.config.js).

**To Reproduce**
Steps to reproduce the behavior:
1. Clone this repo
2. Attempt to run the `with-storybook` example

**Expected behavior**
Storybook example works and provides a reference implementation for `expo` + `storybook`.

**Screenshots**
```
ERR! TypeError: withUnimodules is not a function
ERR! at module.exports (~/expo-examples/with-storybook/.storybook/webpack.config.js:5:10)
```

**Desktop (please complete the following information):**
- OS: macOS
- Browser: N/A - fails in CLI

**Smartphone (please complete the following information):**
- N/A