Webpack Support for Content Security Policy using hashes

### Pre-flight checklist

- [x] I have read the [contribution documentation](https://github.com/electron/forge/blob/main/CONTRIBUTING.md) for this project.
- [x] I agree to follow the [code of conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project uses.
- [x] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

### Problem description

I am working on an Electron app that uses Electron-Forge and Webpack. It is a React app that used Styled-Components. Due to Styled-Components being deprecated there will be work to move away from it. However, in the meantime there is need for it to be supported.

I added a content-security policy for electron using the:
```
session.defaultSession.webRequest.onHeadersReceived
```

I am using a custom protocol as outlined in [Electron Security](https://www.electronjs.org/docs/latest/tutorial/security#18-avoid-usage-of-the-file-protocol-and-prefer-usage-of-custom-protocols). My current content-security policy is `default-src ${CUSTOM_PROTOCOL}: 'unsafe-inline'`.

I would like the ability to not have to `unsafe-inline`. My understanding is that to remove it I would need to use either a nonce or a hash. It seems that a nonce is likely not a good approach for [styled-components](https://github.com/styled-components/styled-components/issues/4258) or [webpack](https://github.com/slackhq/csp-html-webpack-plugin/issues/82#issuecomment-823563459). It seems that using a hash and `dynamic-strict` would be the only potential avenue to improving CSP.

I am requesting a feature that allows for the adding a CSP with hash of the underlying scripts. This should allow me to improve my CSP.

### Proposed solution

There is an existing webpack component that should allow for CSP to be added with script hashes. https://github.com/slackhq/csp-html-webpack-plugin

Just not clear if the repository is supported enough to be used in Electron-Forge or better to implement directly

### Alternatives considered

Nonce seems to not be supported by styled-components

### Additional information

```
"@electron-forge/cli": "^7.7.0",
"electron": "37.1.0",
```

Please let me know if my understanding of content-security policy is correct. This is a new area for me and just trying to ensure I am following best practices.