fix(prometheus): remove conflicting OTLP features and fix datasource URL

- Remove otlp-deltatocumulative (conflicts with otlp-native-delta-ingestion)
- Add /prometheus path to datasource URL (matches routePrefix config)

Author: batazor

ops/Helm/addons/observability/prometheus-operator/prometheus.values.yaml

@@ -40,7 +40,6 @@ kube-prometheus-stack:
         - native-histograms
         - promql-experimental-functions
         - promql-duration-expr
-        - otlp-deltatocumulative
         - otlp-native-delta-ingestion
 
     ingress:

ops/Helm/addons/observability/prometheus-operator/templates/grafana/datasources/prometheus-datasource.yaml

@@ -11,7 +11,7 @@ stringData:
       - name: Prometheus
         uid: prometheus
         type: prometheus
-        url: http://prometheus-prometheus.prometheus-operator.svc:9090
+        url: http://prometheus-prometheus.prometheus-operator.svc:9090/prometheus
         access: proxy
         isDefault: true
         jsonData: