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.

apps/overlays/au-syd1/grafana-system/kustomization.yaml

@@ -0,0 +1,16 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+namespace: grafana-system
+
+resources:
+  - ../../../base/grafana-system
+
+helmCharts:
+  - name: grafana-operator
+    repo: https://artifactapi.k8s.syd1.au.unkin.net/api/v1/virtual/helm
+    version: "5.24.0"
+    releaseName: grafana-operator
+    namespace: grafana-system
+    valuesFile: values.yaml