Add #[debug_middleware] (#2725)

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

axum-macros/tests/debug_middleware/pass/basic.rs

@@ -0,0 +1,13 @@
+use axum::{
+    extract::Request,
+    response::Response,
+    middleware::Next,
+    debug_middleware,
+};
+
+#[debug_middleware]
+async fn my_middleware(request: Request, next: Next) -> Response {
+    next.run(request).await
+}
+
+fn main() {}