fix(kafka): activate NR app in standalone producer (no-transaction path)

Call app.activate() when transaction is None so the agent connects to
the collector and record_custom_metric actually sends data.

Author: shashank-reddy-nr

newrelic/hooks/messagebroker_kafkapython.py

@@ -54,6 +54,16 @@ def wrap_KafkaProducer_send(wrapped, instance, args, kwargs):
     transaction = current_transaction()
 
     if transaction is None:
+        app = application_instance()
+        if not app.active:
+            app.activate()
+        servers = instance.config.get("bootstrap_servers", []) if hasattr(instance, "config") else []
+        if app.active and servers:
+            cache_key = _bootstrap_cache_key(servers)
+            cluster_id = _kafka_cluster_id_cache.get(cache_key)
+            if cluster_id:
+                topic = (_bind_send(*args, **kwargs)[0] or "Default")
+                app.record_custom_metric(KAFKA_CLUSTER_METRIC_PRODUCE.format(cluster_id, topic), 1)
         return wrapped(*args, **kwargs)
 
     topic, value, key, headers, partition, timestamp_ms = _bind_send(*args, **kwargs)