How to test subscriptions?

I'm getting "socket closed" with or without config with `import { ws } from 'msw'`.

Piece of my `.storybook/preview.tsx`:
```
parameters: {
msw: {
handlers: {
graphql: createHandlerFromSchema(...)
}
},
```

Looks like `createHandlerFromSchema` already integrates with MSW but not for subscriptions, is that a bug? And somehow even if I try to configure `msw.ws.link(...)` it still has no effect. Either way please add an example to this repo

storybook params come from https://github.com/mswjs/msw-storybook-addon

I set up resolver for subscription query via `rxjs.Subject` that gets kicked off by calling a mutation (couldn't use `PubSub` from your demo because it has no built-in impl for browser and I already have rxjs). But I don't think that matters.

Start with the `.storybook/preview.tsx` configuration and the repository's existing subscription demo, then reproduce the `socket closed` behavior with `createHandlerFromSchema` and compare it with `msw.ws.link(...)`. Done means the repository includes a working browser subscription example using the described setup and demonstrates how a mutation-triggered `rxjs.Subject` update is handled.

Written by the indexing model from the issue text.