fix: add Kafka environment variables and make topic replicas configurable

- Add WATERMILL_KAFKA_BROKERS, WATERMILL_KAFKA_CLIENT_ID, WATERMILL_KAFKA_CONSUMER_GROUP to metadata values.yaml
- Update metadata values.schema.json to include new Kafka env vars
- Make Kafka topic replicas configurable in link chart (default: 3 for production)
- Add kafka.topics section to link values.yaml with partitions, replicas, retention settings

Author: batazor

boundaries/link/ops/link/templates/kafka.yaml

@@ -10,11 +10,11 @@ metadata:
   labels:
     strimzi.io/cluster: shortlink
 spec:
-  partitions: 1
-  replicas: 1
+  partitions: {{ .Values.kafka.topics.partitions | default 1 }}
+  replicas: {{ .Values.kafka.topics.replicas | default 3 }}
   config:
-    retention.ms: 7200000 # 2 hours
-    segment.bytes: 31457280 # 30MB
+    retention.ms: {{ .Values.kafka.topics.retention.ms | default 7200000 }}
+    segment.bytes: {{ .Values.kafka.topics.segment.bytes | default 31457280 }}
 ---
 # LinkUpdated event topic - canonical name: link.link.updated.v1
 # Follows ADR-0002 canonical event naming standard
@@ -26,11 +26,11 @@ metadata:
   labels:
     strimzi.io/cluster: shortlink
 spec:
-  partitions: 1
-  replicas: 1
+  partitions: {{ .Values.kafka.topics.partitions | default 1 }}
+  replicas: {{ .Values.kafka.topics.replicas | default 3 }}
   config:
-    retention.ms: 7200000 # 2 hours
-    segment.bytes: 31457280 # 30MB
+    retention.ms: {{ .Values.kafka.topics.retention.ms | default 7200000 }}
+    segment.bytes: {{ .Values.kafka.topics.segment.bytes | default 31457280 }}
 ---
 # LinkDeleted event topic - canonical name: link.link.deleted.v1
 # Follows ADR-0002 canonical event naming standard
@@ -42,9 +42,9 @@ metadata:
   labels:
     strimzi.io/cluster: shortlink
 spec:
-  partitions: 1
-  replicas: 1
+  partitions: {{ .Values.kafka.topics.partitions | default 1 }}
+  replicas: {{ .Values.kafka.topics.replicas | default 3 }}
   config:
-    retention.ms: 7200000 # 2 hours
-    segment.bytes: 31457280 # 30MB
+    retention.ms: {{ .Values.kafka.topics.retention.ms | default 7200000 }}
+    segment.bytes: {{ .Values.kafka.topics.segment.bytes | default 31457280 }}
 {{- end }}

boundaries/link/ops/link/values.yaml

@@ -112,6 +112,17 @@ service:
       protocol: TCP
       public: true
 
+# ==============================================================================
+# Kafka topics configuration
+kafka:
+  topics:
+    partitions: 1
+    replicas: 3 # Minimum replicas for production Kafka cluster
+    retention:
+      ms: 7200000 # 2 hours
+    segment:
+      bytes: 31457280 # 30MB
+
 # ==============================================================================
 # Prometheus Operator ServiceMonitor configuration
 monitoring: