[hotfix] Add new kube-system to kube-prometheus-stack (!114)

Reviewed-on: https://git.avroid.tech/K8s/k8s-configs/pulls/114
Reviewed-by: Rustam Tagaev <rustam.tagaev@avroid.team>

clusters/k8s-avroid-office.prod.local/namespaces/kube-prometheus-stack/kube-prometheus-stack/argocd-apps-kube-prometheus-stack-app.yaml

@@ -68,3 +68,7 @@ spec:
       kind: ServiceMonitor
     - group: '*'
       kind: Prometheus
+  # When using Applications-in-any-namespace, this field determines which namespaces this AppProject permits
+  # Applications to reside in. Details: https://argo-cd.readthedocs.io/en/stable/operator-manual/app-any-namespace/
+  sourceNamespaces:
+    - "kube-system"