[Docs] Non-trivial Axum example

It would be nice in the Axum example under `/examples` to include a route handler that has more real-world use cases, like calling into another async function such as in API -> Service -> Repository layers. I think documentation on the `#[worker::send]` workaround included under the Axum example section would be incredibly helpful to save frustration, and improve adoption of cf workers Other issues that mention bugs that are fixed by #[worker::send]: #485 This workaround is mentioned under src/lib.rs in cargo docs for the crates.io entry, but having it included in the actual Axum example would be great. I can open a PR later for this docs update if it makes sense for the team. Cheers!