fix: update README and HelmRelease patch for cert-manager configuration

flux/infrastructure/infra-devops/post/helmrelease-cert-manager-patch.yaml

@@ -10,6 +10,15 @@ metadata:
     kustomize.toolkit.fluxcd.io/prune: disabled
 spec:
   interval: 30m
+  chart:
+    spec:
+      chart: cert-manager
+      version: v1.19.3
+      sourceRef:
+        kind: HelmRepository
+        name: jetstack
+        namespace: infra-gitops
+      interval: 12h
   values:
     prometheus:
       servicemonitor: