docs(kubernetes): bump cert-manager to v1.20.3

Author: mesutoezdil

docs/kubernetes/managing-certificates.mdx

@@ -30,7 +30,7 @@ Install cert-manager from the OCI registry with CRD support enabled:
 
 ```shell
 helm upgrade --install cert-manager oci://quay.io/jetstack/charts/cert-manager \
-  --version v1.20.2 \
+  --version v1.20.3 \
   --namespace cert-manager \
   --create-namespace \
   --set crds.enabled=true \