feat(data): OpenSearch prometheus-exporter sidecar

elasticsearch-exporter v1.7.0 runs as a sidecar, scrapes localhost:9200,
exposes elasticsearch_* metrics on :9114. ServiceMonitor re-enabled.
Alert rules updated to use elasticsearch_* metric names.
Flags: --es.all --es.indices --es.shards --collector.clustersettings

base/data/opensearch-alertrules.yaml

@@ -10,7 +10,7 @@ spec:
     - name: opensearch
       rules:
         - alert: OpenSearchClusterRed
-          expr: opensearch_cluster_health_status{color="red"} == 1
+          expr: elasticsearch_cluster_health_status{color="red"} == 1
           for: 2m
           labels:
             severity: critical
@@ -19,7 +19,7 @@ spec:
             description: "OpenSearch cluster {{ $labels.cluster }} health status is red."
 
         - alert: OpenSearchClusterYellow
-          expr: opensearch_cluster_health_status{color="yellow"} == 1
+          expr: elasticsearch_cluster_health_status{color="yellow"} == 1
           for: 10m
           labels:
             severity: warning
@@ -28,10 +28,10 @@ spec:
             description: "OpenSearch cluster {{ $labels.cluster }} health status is yellow."
 
         - alert: OpenSearchHeapHigh
-          expr: (opensearch_jvm_mem_heap_used_bytes / opensearch_jvm_mem_heap_max_bytes) > 0.85
+          expr: (elasticsearch_jvm_memory_used_bytes{area="heap"} / elasticsearch_jvm_memory_max_bytes{area="heap"}) > 0.85
           for: 5m
           labels:
             severity: warning
           annotations:
             summary: "OpenSearch JVM heap usage is high"
-            description: "OpenSearch node {{ $labels.node }} in {{ $labels.namespace }} heap usage is above 85%."
+            description: "OpenSearch node {{ $labels.name }} in {{ $labels.namespace }} heap usage is above 85%."