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-service.yaml

@@ -17,3 +17,7 @@ spec:
       port: 9300
       targetPort: 9300
       protocol: TCP
+    - name: metrics
+      port: 9114
+      targetPort: 9114
+      protocol: TCP