Allow to configure callback for replay network body handling

We may want to add a callback configuration option for replay, that allows users to manually strip stuff from network bodies client side.

An example API could be:

```ts
new Replay({
  network: {
    urls: ['https://my-domain.com'],
    requestBodyCallback: (body: unknown) => unknown,
    responseBodyCallback: (body: unknown) => unknown,
  }
})
```