Add logging of JSON requests.

src/main.rs

@@ -52,7 +52,9 @@ async fn echo_request(
             warn!("Received a non-JSON body.");
             None
         },
-        Some(Json(value)) => Some(value),
+        Some(Json(value)) => {
+            info!("JSON request: {}", value.to_string());
+            Some(value)},
     };
     let response = EchoResponse {
         method,