[MINDEXER-239] Better HTTP error messages (#386)

Slightly improve it, at least give some hint from where
and what we got. note: Java 11 HttpClient does NOT
expose reason phrase

---

https://issues.apache.org/jira/browse/MINDEXER-239

search-api/src/main/java/org/apache/maven/search/api/transport/Java11HttpClientTransport.java

@@ -70,6 +70,11 @@ public void close() throws IOException {
                 inputStream.close();
             }
         }
+
+        @Override
+        public String toString() {
+            return response.uri() + " -> " + response.version() + " " + response.statusCode();
+        }
     }
 
     private final Duration timeout;