feat(cert-manager): include cert-manager release manifest in kustomization (#34)

### Summary of Changes

- Added
`https://github.com/cert-manager/cert-manager/releases/download/v1.17.0/cert-manager.yaml`
to `ci/k8s/infrastructure/cert-manager/kustomization.yaml` so
cert-manager installs automatically via Flux GitOps.

ci/k8s/infrastructure/cert-manager/kustomization.yaml

@@ -1,4 +1,5 @@
 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
+  - https://github.com/cert-manager/cert-manager/releases/download/v1.17.0/cert-manager.yaml
   - cluster-issuer.yaml