feat: migrate cert-manager from Terraform to ArgoCD (#42)

- Add cert-manager base ArgoCD application with namespace, RBAC resources
- Create cert-manager overlay for au-syd1 with Helm chart configuration
- Update platform ApplicationSet to include cert-manager deployment
- Configure cert-manager v1.19.2 with jetstack Helm repository
- Maintain one-to-one migration from Terraform configuration

Reviewed-on: #42

apps/base/cert-manager/clusterrole.yaml

@@ -0,0 +1,12 @@
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  name: cert-manager-vault-token-creator
+  labels:
+    app.kubernetes.io/name: "cert-manager-config"
+    app.kubernetes.io/instance: "cert-manager-config"
+rules:
+- apiGroups: [""]
+  resources: ["serviceaccounts/token"]
+  verbs: ["create"]