grafana: deploy Grafana instance, datasource and dashboards

Deploys Grafana in the observability project via the grafana-operator,
mirroring the puppet Grafana but modernised: CNPG for state and Authentik
OIDC for auth. Ports the live datasource + dashboards in as CRs.

Changes (apps/base/grafana):
- CNPG postgres Cluster + rw Pooler (db grafana), plus VaultAuth +
  VaultStaticSecrets pulling postgres/oauth credentials from Vault.
- Grafana CR: postgres backend via the pooler, Authentik generic_oauth
  (client id/secret from the Vault-synced secret, openid/email/profile
  scopes, group->role mapping), root_url grafana.k8s.syd1.au.unkin.net.
- Single GrafanaDatasource (k8s VictoriaMetrics via the operator vmselect
  service); reuses the previous default datasource uid so imported
  dashboards resolve without edits.
- 13 GrafanaDashboards (gzipJson) exported from the current grafana.
- Gateway API (traefik-internal) + HTTPRoute for grafana.k8s.syd1.au.unkin.net.
- Register apps/overlays/*/grafana in the observability ApplicationSet and
  add the grafana namespace to the project destinations.

apps/base/grafana/httproute.yaml

@@ -0,0 +1,55 @@
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: grafana-http-redirect
+  namespace: grafana
+  labels:
+    app.kubernetes.io/name: grafana
+    app.kubernetes.io/instance: grafana
+spec:
+  hostnames:
+    - grafana.k8s.syd1.au.unkin.net
+  parentRefs:
+    - group: gateway.networking.k8s.io
+      kind: Gateway
+      name: grafana
+      sectionName: http
+  rules:
+    - filters:
+        - type: RequestRedirect
+          requestRedirect:
+            scheme: https
+            statusCode: 301
+      matches:
+        - path:
+            type: PathPrefix
+            value: /
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: grafana
+  namespace: grafana
+  labels:
+    app.kubernetes.io/name: grafana
+    app.kubernetes.io/instance: grafana
+spec:
+  hostnames:
+    - grafana.k8s.syd1.au.unkin.net
+  parentRefs:
+    - group: gateway.networking.k8s.io
+      kind: Gateway
+      name: grafana
+      sectionName: https
+  rules:
+    - backendRefs:
+        - group: ""
+          kind: Service
+          name: grafana-service
+          port: 3000
+          weight: 1
+      matches:
+        - path:
+            type: PathPrefix
+            value: /