When the control plane has lots of namespaces, the namespace list is taking too long to be generated.

On Kiali side, we observed the getNamespaceList can take 5 seconds with 2 namespaces on a control plane

Some spikes of 5, 10 and even 20 seconds were observed with more namespaces

Testing information:

https://docs.google.com/presentation/d/1ZhKzsvu4iJNUHsnieVUEOYDV797Y40dSuPpjFF5sFJc/edit?usp=sharing

Possibly related to kubernetes cache.