Support air-gapped installation

[sancho21]

I'm trying to install it in an air-gapped environment (no internet access available). In order to do the installation I prefer Helm chart, but I have to pass variable this way:

helm install -n openelb-system --create-namespace openelb openelb-*.tgz --set admission.image.repository=repository:5000/kubespheredev/kube-webhook-certgen --set manager.image.repository=repository:5000/kubesphere/openelb

I'd be good if there's a possibility to do like most people do --set global.imageRegistry=myprivate-docker-registry.local:5000 variable

Another thing is, somehow I found that the chart doesn't explicitly show the need of aledbf/kube-keepalived-vip:0.35 (it's not visible in helm template command). So, I have to download the image after kubectl shows that OpenELB needs it. Moreover, there's no way to override the image registry location. No option to do something like --set keepalived.image.repository=repository:5000/aledbf/kube-keepalived-vip:0.35

In the end, I still failed to make use of OpenELB in my air-gapped environment