Add kube-prometheus-stack example

[Pro]

I am currently trying to familiarize myself with flux, and face some issues getting the prometheus stack running inside this multi tenancy repo.

I tried to add the Monitoring stack as described in https://fluxcd.io/flux/guides/monitoring/ by creating the corresponding flux files.
And I feel quite stuck, especially with setting correct RBAC and namespaces. I played around with a lot of different settings, but was not able to get the monitoring stack up and running.

Here is the diff of the files:
main...Pro:flux2-multi-tenancy:monitoring

The reconciliation of kube-prometheus-stack fails with:

error Kustomization/kube-prometheus-stack.flux-system - Reconciliation failed after 68.004611ms, next try in 1h0m0s Namespace/monitoring dry-run failed, reason: Forbidden: namespaces "monitoring" is forbidden: User "system:serviceaccount:flux-system:monitoring-sa" cannot patch resource "namespaces" in API group "" in the namespace "monitoring"

Could you please point me to the right direction on how to add the monitoring stack?