Add the postgrescluster helm chart to the OCI developer registry

[Inigo4562]

Overview

Currently only the postgres operator helm chart can be found in the OCI developer registry (oci://registry.developers.crunchydata.com/crunchydata/pgo). It would be great to also be able pull the postgrescluster helm chart from that same registry.

Use Case

This will allow testing with this chart without having to clone the examples github repository.

Desired Behavior

Download the postgrescluster chart with the following command:

helm pull oci://registry.developers.crunchydata.com/crunchydata/postgrescluster