[porter/mattermost-aks] Helm stable repo fails to fetch

[tlaur]

Install fails after trying to fetch https://kubernetes-charts.storage.googleapis.com/index.yaml as the URL is outdated. Correct location AFAIK should be https://charts.helm.sh/stable/

Hang tight while we grab the latest from your chart repositories...
...Skip local chart repository
...Successfully got an update from the "ingress-nginx" chart repository
...Successfully got an update from the "jetstack" chart repository
...Unable to get an update from the "stable" chart repository (https://kubernetes-charts.storage.googleapis.com):
Failed to fetch https://kubernetes-charts.storage.googleapis.com/index.yaml : 403 Forbidden

[carolynvs]

The helm mixin was only for helm v2 which is deprecated. The fix for this error is to use the helm3 mixin instead.