Add Kafka output metrics (#42537) (#42557)

(cherry picked from commit 2b8d554)

Co-authored-by: William Easton <[email protected]>

libbeat/outputs/kafka/config.go

@@ -306,11 +306,14 @@ func newSaramaConfig(log *logp.Logger, config *kafkaConfig) (*sarama.Config, err
 	k.Version = version
 
 	k.Producer.Partitioner = partitioner
+
 	k.MetricRegistry = adapter.GetGoMetrics(
 		monitoring.Default,
-		"libbeat.outputs.kafka",
-		adapter.Rename("incoming-byte-rate", "bytes_read"),
-		adapter.Rename("outgoing-byte-rate", "bytes_write"),
+		"libbeat.outputs",
+		adapter.Rename("incoming-byte-rate", "read.bytes"),
+		adapter.Rename("outgoing-byte-rate", "write.bytes"),
+		adapter.Rename("request-latency-in-ms", "write.latency"),
+		adapter.Rename("requests-in-flight", "kafka.requests-in-flight"),
 		adapter.GoMetricsNilify,
 	)