fix(grafana): fix config format and set dashboard selector

otc/observability.think-ahead.cloud/stacks/observability/grafana-operator/manifests/grafana.yaml

@@ -12,6 +12,7 @@ spec:
       resources:
         requests:
           storage: 10Gi
-  plugins:
-    - victoriametrics-metrics-datasource
-    - victoriametrics-logs-datasource
+  config:
+    plugins:
+      - victoriametrics-metrics-datasource
+      - victoriametrics-logs-datasource

otc/observability.think-ahead.cloud/stacks/observability/grafana-operator/manifests/ingress-nginx.yaml

@@ -3,4 +3,7 @@ kind: GrafanaDashboard
 metadata:
   name: ingress-nginx 
 spec:
+  instanceSelector:
+    matchLabels:
+      dashboards: "grafana"
   url: "https://grafana.com/api/dashboards/1860/revisions/30/download"