Render the release-prefixed cluster host in the LabKit-format PostgreSQL Secret

What we need

The LabKit-format PostgreSQL Secret must point at the Service the chart actually creates when the release has a name.

Why

The Secret renders host from $cluster.name (cluster-secrets.yaml#L54) while the CloudNativePG Cluster, its Service and the -conn Secret use the release-prefixed $clusterName (#L36). With a non-empty release name the contract-shaped Secret names a Service that does not exist. #4 (closed) added the prefix to the Secret names but not to the host value.

The Relay fragment on the gitlab-caproni rig works around it with a CUSTOM projection onto the -conn Secrets (gitlab-org/gitlab-caproni!108 (closed)).