grafana-system: deploy grafana-operator

Adds the grafana-operator (grafana.integreatly.org CRDs + controller) so
Grafana and its dashboards/datasources can be managed declaratively as
CRs in a follow-up PR. Sits in the platform project like the other
operators (vm-system, cnpg-system).

Changes:
- Add grafana-system namespace + grafana-operator helm chart v5.24.0
  (watches all namespaces).
- Render CRDs inline (crds.immutable: false) so ArgoCD installs/manages
  the 13 grafana.integreatly.org CRDs instead of the skipped helm crds/
  subchart.
- Register apps/overlays/*/grafana-system in the platform ApplicationSet.

argocd/applicationsets/platform.yaml

@@ -23,6 +23,7 @@ spec:
       - path: apps/overlays/*/elastic-system
       - path: apps/overlays/*/encapi
       - path: apps/overlays/*/externaldns
+      - path: apps/overlays/*/grafana-system
       - path: apps/overlays/*/inteldeviceplugins-system
       - path: apps/overlays/*/jfrog
       - path: apps/overlays/*/kanidm