Consider publishing helm chart artifacts to Github

Created by: caugustus-sourcegraph

When the helm chart repository moved to helm.sourcegraph.com we stopped pushing to GH Pages. This also stopped creating releases (https://github.com/sourcegraph/deploy-sourcegraph-helm/releases). It could be nice to re-enable that publishing step, so it's immediately obvious which versions are available / make it easy to download manually instead of through helm.