Add support for https://artifacthub.io/

[scovetta]

We should think about adding support for Artifact Hub:

API docs: https://artifacthub.io/docs/api/

Example URL: https://artifacthub.io/api/v1/packages/helm/ingress-nginx/ingress-nginx

$ curl -s 'https://artifacthub.io/api/v1/packages/helm/ingress-nginx/ingress-nginx' | jq -r .content_url
https://github.com/kubernetes/ingress-nginx/releases/download/helm-chart-4.11.2/ingress-nginx-4.11.2.tgz