kele-list: allow switching namespace from existing list buffer

[jinnovation]

When a user enters a kele-list buffer, the end result is largely static. In order to view any new
combination of context/namespace/kind, the user needs to kele-list again and bring up an entirely
separate buffer -- one that, in terms of functionality, is largely the same.

What we would like, instead, is for the user to hit n in a kele-list-mode buffer and be able to
select a new namespace to list the existing kind in. This would make a good incremental step
towards kele-list-mode buffers being able to act as a cluster "overview," similar to the "status"
view that kubernetes-el is built around.

Completion Criteria

• Keybinding to switch the desired namespace
• Refresh the buffer on switch
• Rename the buffer to reflect the new namespace selection