Document proper use of overrides

We have https://docs.openappstack.net/en/v0.7/customizing.html#example-customize-nextcloud-to-work-with-staging-certificates but it's shortcoming in the way that i.e. for nextcloud, simply adding an override is not enough when an application is already installed. So we need to document what needs to happen in this case.

I.e.:

• apply override
• reconcile kustomization
• in nextcloud, the configure_apps job is run as an post-upgrade hook so we need to ensure NC is upgraded by the steps above

added Documentation + 1 deleted label

changed milestone to %Future

removed 1 deleted label

In my experiments just now, after changing the override configmap, flux reconcile ks $RESOURCE doesn't have an effect, while flux reconcile hr $NAMESPACE $RESOURCE does let helm-controller reinstall the release with the new values.