Shared configuration for Backstage instances

[gusevda]

Some Backstage configuration should be shared between all backstage instances. How can we achieve this with current deployment approach to MCs?

One configuration is gs.adminGroups - https://github.com/giantswarm/giantswarm-management-clusters/blob/main/management-clusters/gazelle/extras/backstage/backstage-app-config.yaml#L323-L325

Another one is gs.kubernetesVersions which should be also kept up to date.

For Happa we use the same configurations and the source for them is in the shared-configs repo:
https://github.com/giantswarm/shared-configs/blob/main/include/k8s-versions.yaml.template
https://github.com/giantswarm/shared-configs/blob/main/default/apps/happa/configmap-values.yaml.template#L79