[sophora-dashboard] introduce global value for "registry"

[muffl0n]

Makes it much easier to override the default registry. Otherwise one would have to override each and every declaration of repository. Far worse, new entries would go undetected if not checked externally with e.g. Kyverno.

This change should be applied to all charts.

kube-prometheus-stack has a similar approach leveraging global.imageRegistry: https://github.com/prometheus-community/helm-charts/blob/main/charts/kube-prometheus-stack/values.yaml#L223

[muffl0n]

On a second thought: We should probably add something like this

registries: 
  subshell: docker.subshell.com

instead of simply

registry: docker.subshell.com

so that we can add third-party registries more easily:

registries: 
  subshell: docker.subshell.com
  quay: quay.io

[philmtd]

I did not see this anywhere else, and I doubt that there is much benefit. I understand all this intends to do is to make it easier to replace a registry with a proxy, which now would require two lines instead of one, right? I'd rather vote to close this and leave it as it is. kube-prometheus-stack has way more than two images it pulls, so I think it's more justified there.

[muffl0n]

Importer is pulling three images, server is pulling four.
But I get your point and would be okay with closing this PR.

[muffl0n]

Btw, Bitnami does it too: https://github.com/bitnami/charts/blob/2e7963d2d87378f84f3f58d792b74a831858f9e3/bitnami/common/templates/_images.tpl#L18

[philmtd]

Okay. I think we could do a section like this:

global:
  imageRegistry: ""

This is what Bitnami and KPS do and what seems to be the most standard way of doing it.

[muffl0n]

Changed the PR to reflect this.