Use actix-web 4

[ctron]

Although actix-web 4 is only released as beta yet, it is required for the switch to tokio 1.

[slinkydeveloper]

I see it's still in beta https://github.com/actix/actix-web/releases/tag/web-v4.0.0-beta.1, I would love to wait for the final release before updating it here. How does it sounds?

[andrewwebber]

Also observing this, would be great to have a branch somewhere to test. For example using OpenTelemetry in Rust requires Tokio1 and I would love to confirm that OpenTel + ActixWeb + Cloudevents = ❤️

[andrewwebber]

@ctron Thank you for putting together your fork