Provide values override for `global.clusterRouterBase`

[tumido]

In the helm chart install instructions we require the following step:

https://github.com/janus-idp/helm-backstage/tree/main/charts/backstage#installing-from-the-chart-repository

When installed on OpenShift via this operator, this should be automated:

1. Make the operator fetch oc get ingresses.config/cluster -o jsonpath={.spec.domain}
2. Provide this via reconciler.WithOverrideValues

Please make the operator to always enforce this value to be in sync with the cluster - The operator doesn't need to watch the ingresses.config/cluster resource, but it should fetch the correct value on every helm upgrade.

[kadel]

2. Provide this via reconciler.WithOverrideValues

I'm not sure if using WithOverridValues is the right thing. With this approach, the values will only be updated when the operator starts. I'm unable to figure out how to update values for WithOverridValues on every helm upgrade.

I think that there should be a little bit more than just simply overriding global.clusterRouterBase.

For example, users might want to set their own custom clusterRouterBase that doesn't match the default Ingress domain.
I'm considering the approach where global.clusterRouterBase is set only when the user has not set it explicitly.