Add #[debug_middleware] (#2725)

Co-authored-by: David Pedersen <[email protected]>

axum-macros/tests/debug_middleware/fail/takes_next_twice.rs

@@ -0,0 +1,9 @@
+use axum::{debug_middleware, extract::Request, middleware::Next, response::Response};
+
+#[debug_middleware]
+async fn my_middleware(request: Request, next: Next, next2: Next) -> Response {
+    let _ = next2;
+    next.run(request).await
+}
+
+fn main() {}