Add Authentik identity provider deployment

- CNPG PostgreSQL cluster (3 instances) with rw and ro poolers (2 instances each)
- Redis with persistent storage
- Gateway API: identity.unkin.net (HTTPS) + LDAPS via TLSRoute on ldap.k8s.syd1.au.unkin.net and ldap.main.unkin.net
- HTTPRoute for external-dns record creation on LDAP hostnames
- Vault secrets: postgres-credentials, authentik-credentials, s3-credentials
- S3 storage via RadosGW
- Helm chart authentik 2026.5.3 with 3 server replicas, 2 worker replicas
- Woodpecker ServiceAccount for terraform-authentik CI
- Platform applicationset and project updated

apps/overlays/au-syd1/authentik/kustomization.yaml

@@ -0,0 +1,14 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - ../../../base/authentik
+
+helmCharts:
+  - name: authentik
+    repo: https://artifactapi.k8s.syd1.au.unkin.net/api/v1/virtual/helm
+    version: "2026.5.3"
+    releaseName: authentik
+    namespace: authentik
+    valuesFile: values.yaml