fix: make grafana prometheus datasource resilient with nodeport fallback

ansible/roles/observability-content/templates/grafana-default-prometheus-datasource.yaml.j2

@@ -0,0 +1,26 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: kube-prometheus-stack-grafana-datasource
+  namespace: {{ observability_namespace }}
+data:
+  datasource.yaml: |-
+    apiVersion: 1
+    datasources:
+    - name: "Prometheus"
+      type: prometheus
+      uid: prometheus
+      url: {{ grafana_prometheus_effective_url }}/
+      access: proxy
+      isDefault: true
+      jsonData:
+        httpMethod: POST
+        timeInterval: 30s
+    - name: "Alertmanager"
+      type: alertmanager
+      uid: alertmanager
+      url: http://kube-prometheus-stack-alertmanager.{{ observability_namespace }}:9093/
+      access: proxy
+      jsonData:
+        handleGrafanaManagedAlerts: false
+        implementation: prometheus