De-duplicate `config.yaml` and `secret-config.yaml`

It seems there are near-identical two configuration files:
* https://github.com/kellnr/helm/blob/main/charts/kellnr/templates/secret-config.yaml
* https://github.com/kellnr/helm/blob/main/charts/kellnr/templates/config.yaml

I think there should be a way to dedup all that