Fix user guide for Istio Vault CA integration (#4069)
Fix user guide for Istio Vault CA integration (#4069)

The user guide for Istio Vault CA integration fails
because the cluster hosting an example Vault server was deleted.
This PR fixes the user guide with a new example Vault CA.
istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io