feat: exposing `onMessage` as a prop

[remarkablemark]

Thanks for your work on this library! Is it possible to expose onMessage as a callback prop similar to how on the web, you can listen to Chatwoot messages and hook in your own custom functionality?

[rmc-softdev]

+1 to the above request. In theory, we should be able to have access to the underlying listeners for the WebView component as if we were in the web, e.g., chat opened, etc.