feat: Add cert-manager as dependency for Rancher

Rancher requires cert-manager when managing its own TLS (not tls:external).
Added cert-manager HelmRelease with CRDs enabled.

infrastructure/addons/kustomization-cert-manager.yaml

@@ -0,0 +1,15 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: addon-cert-manager
+  namespace: flux-system
+spec:
+  interval: 10m
+  prune: true
+  sourceRef:
+    kind: GitRepository
+    name: platform
+  path: ./infrastructure/addons/cert-manager
+  wait: true
+  timeout: 10m
+  suspend: false