Description of problem:

The list is currently hard-coded in https://github.com/redhat-developer/rhdh-chart/blob/main/charts/backstage/templates/_partials.tpl

Making it configurable in the values file will make it easier for users to support alternate registries more easily. Or even for us, to quickly test new versions or packages of these plugins without changing the Chart itself.
Otherwise, we need to update the Chart to make such changes.