Try to kill kubel buffer after prompting for new the context

[murshies]

When calling kubel-set-context from the main kubel buffer, killing the kubel buffer prior to asking for the new context results in the default-directory of the prompt being the default-directory of whichever buffer takes the place of the kubel buffer. This can cause issues if the new buffer is remote via tramp, which can often be the case with kubel. An example workflow where this is an issue:

1. Execute an action on a pod, for example opening a shell to a container
2. After establishing the TRAMP connection to the container, switch back to the main kubel buffer in the same window
3. Invoke kubel-set-context

With the current implementation, the kubel buffer will be killed, putting the container shell at the foreground of the window. The kubel--exec-to-string is invoked through the TRAMP connection, and none of the existing contexts are available for selection.

With this change, the kubel--exec-to-string is executed with the default-directory of the existing kubel buffer, and the correct contexts will be available.

[murshies]

This is such a great quality of life improvement! Thank you!

Thanks! I use this basically every day so I appreciate this project a lot!