adapt to bitnami stopping the publication of charts on a Helm repo

Since today, we've observed failures in our push-helm-artifact and renovate jobs, that can't retrieve Bitnami help charts anymore (or at least not reliably).

--- processing unit gitea-postgresql-ha 00:30
2024-12-16 10:16:21,082 [INFO] - processing version 14.2.30 from sylva-units values
2024-12-16 10:16:21,082 [INFO] helm pull --repo https://charts.bitnami.com/bitnami --version 14.2.30 postgresql-ha -d /tmp/sylva-artifact-hhh1166i
Traceback (most recent call last):
  File "/builds/sylva-projects/sylva-core/tools/oci/push-helm-charts-artifacts.py", line 202, in <module>
    process_chart_in_helm_repo(
  File "/builds/sylva-projects/sylva-core/tools/oci/push-helm-charts-artifacts.py", line 99, in process_chart_in_helm_repo
    if subprocess.run(f"helm pull --repo {helm_repo} --version {chart_version} {chart_name}"
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/subprocess.py", line 571, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command 'helm pull --repo https://charts.bitnami.com/bitnami --version 14.2.30 postgresql-ha -d /tmp/sylva-artifact-hhh1166i' returned non-zero exit status 1.

(verbosity added by a "debug" commit in 573e8053)

This is due to Bitnami having recently stopped the publication of their Helm charts from the https://charts.bitnami.com/bitnami repo. The announcement is here. The new advertised way to consume their charts is via OCI artifacts.

We need to:

• evolve our toolbox to allow sylva-units and our tools/oci script to use upstream OCI artifacst as the source
• or consume the Bitnami charts from Git