Add K8s namespace/context to Wave Prompt

[sawka]

Wave should track the current k8s namespace/context in the prompt.

[sawka]

Implemented this in v0.7.3, but I had to remove it after we had reports of a big performance issue querying the k8s context/namespace (up to 5s where Wave was hanging). Will try to make another pass at getting this in -- potentially in an asynchronous way.