feat(observability): add configurable grafana.prometheusDatasourceName to agent chart (#1982)

Closes #1891
  
Adds a grafana.prometheusDatasourceName field to the observability agent
chart values.

The observability agent reaches Prometheus exclusively through the
Grafana MCP tool server.

Tools like query_prometheus take a Grafana datasource name or UID, not a
raw endpoint.
When grafana.prometheusDatasourceName is set, it is injected into the
agent system message so the agent knows which Grafana datasource to use
for Prometheus queries across restarts.

When left empty (default), nothing changes.

---------

Signed-off-by: mesutoezdil <mesudozdil@gmail.com>

Author: mesutoezdil

helm/agents/observability/templates/agent.yaml

@@ -22,6 +22,12 @@ spec:
       - **Kubernetes Observability**: You comprehend service monitoring, resource utilization patterns, and common performance bottlenecks.
       - **Metrics Interpretation**: You can analyze trends, anomalies, and correlations in observability data.
       - **Alerting Design**: You can recommend effective alerting strategies based on metrics and thresholds.
+      {{- with .Values.grafana.prometheusDatasourceName }}
+
+      ## Prometheus Datasource
+
+      Before making any Prometheus tool call, you must first call get_datasource with name "{{ . }}" to resolve the datasource UID. Use that UID for all subsequent Prometheus tool calls (query_prometheus, list_prometheus_metric_names, list_prometheus_label_names, list_prometheus_label_values, list_prometheus_metric_metadata).
+      {{- end }}
 
       {{ `{{include "builtin/kubernetes-context"}}` }}
 
@@ -94,8 +100,7 @@ spec:
           - get_sift_analysis
           - get_oncall_shift
           - get_incident
-          - get_datasource_by_uid
-          - get_datasource_by_name
+          - get_datasource
           - get_dashboard_panel_queries
           - get_dashboard_by_uid
           - get_current_oncall_users

helm/agents/observability/values.yaml

@@ -19,3 +19,8 @@ compaction: {}
 podSecurityContext: {}
 
 securityContext: {}
+
+# -- Optional Grafana datasource name for Prometheus (e.g. "Prometheus"). When set, the agent
+# uses this datasource name for all Prometheus queries instead of discovering it at runtime.
+grafana:
+  prometheusDatasourceName: ""