kafka: Add broker start time metric tagged with broker_id (DataDog#23020)

* kafka: Add broker start time metric tagged with broker_id

Add a new metric kafka.broker.start_time that extracts the broker ID
from the kafka.server:type=app-info,id=<broker_id> JMX bean name and
applies it as a broker_id tag. This is the first Kafka metric to carry
the broker_id tag, enabling per-broker metric correlation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Fix CI: add changelog and assert new broker start_time metric in test

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: piochelepiotr

kafka/changelog.d/23020.added

@@ -0,0 +1 @@
+Add kafka.broker.start_time metric tagged with broker_id.

kafka/datadog_checks/kafka/data/metrics.yaml

@@ -898,3 +898,20 @@ jmx_metrics:
         - tag_name: kafka_cluster_id
           bean_name: kafka.server:type=KafkaServer,name=ClusterId
           attribute: Value
+
+    #
+    # Broker info
+    #
+    - include:
+        domain: 'kafka.server'
+        bean_regex: 'kafka\.server:type=app-info,id=(.*)'
+        attribute:
+          StartTimeMs:
+            metric_type: gauge
+            alias: kafka.broker.start_time
+        tags:
+          broker_id: $1
+      dynamic_tags:
+        - tag_name: kafka_cluster_id
+          bean_name: kafka.server:type=KafkaServer,name=ClusterId
+          attribute: Value

kafka/metadata.csv

@@ -1,4 +1,5 @@
 metric_name,metric_type,interval,unit_name,per_unit_name,description,orientation,integration,short_name,curated_metric
+kafka.broker.start_time,gauge,10,millisecond,,The start time of the Kafka broker in milliseconds since epoch.,0,kafka,broker start time,
 kafka.consumer.bytes_consumed,gauge,10,byte,second,The average number of bytes consumed per second for a specific topic.,1,kafka,con bytes consumed,
 kafka.consumer.bytes_in,gauge,10,byte,second,Consumer bytes in rate.,1,kafka,con bytes in,
 kafka.consumer.delayed_requests,gauge,10,request,,Number of delayed consumer requests.,-1,kafka,con delayed req,

kafka/tests/common.py

@@ -69,4 +69,6 @@
     "kafka.session.fetch.eviction",
     # Listeners
     "kafka.server.socket.connection_count",
+    # Broker
+    "kafka.broker.start_time",
 ]