Replace stable/external-dns by bitnami/external-dns

Replace the current stable/external-dns by bitnami/external-dns due to the Helm stable repository deprecation timeline.

stable/external-dns was a chart contributed by Bitnami to the stable repository, once announced the EOL of this repository, from Bitnami, we followed the required steps to deprecate it, being hosted now in the bitnami repository. In the end, bitnami/external-dns is the same chart but hosted in a different repository and receiving updates since the stable/external-dns was marked as deprecated some months ago, see https://github.com/helm/charts/tree/master/stable/external-dns#this-helm-chart-is-deprecated

+info: &15 (closed)