Add an example that makes use of async operations

[bilelmoussaoui]

Something like sending a web request to retrieve some data and then display it. Maybe using tokio or some other async runtime.

[sdroege]

There's an example in gtk-rs-core and I think also an example for dialogs here?

Maybe using tokio or some other async runtime.

That will involve a bit of boilerplate for the cross-runtime communication then but probably a good idea to have an example for that.

[bilelmoussaoui]

There's an example in gtk-rs-core and I think also an example for dialogs here?

There is indeed, but it doesn't show how to integrate with a window without blocking the main thread

[Claudio-code]

I wrote it example https://github.com/gtk-rs/gtk4-rs/pull/1578 but CI falls because not found openssl dependency https://github.com/gtk-rs/gtk4-rs/actions/runs/7649773189/job/20844748624