Allow for other pod terminal shells in extension config file

[roberto-sebastiano]

Hello,

I see that it seems there is no way of forcing the extension to use a shell different from bash when opening a terminal for a pod from the extension sidebar (Pods -> Pod Name -> Icon Terminal)

From this line, I see that we call the function isBashOnContainer, maybe we could first check if we specified the shell as an option in the extension, like

vs-kubernetes.pod-shell: "zsh"

In that case, use that as an override to "isBashOnContainer"
otherwise, we could rename isBashOnContainer to isShellOnContainer, check for vs-kubernetes.pod-shell value, if that option is missing, then check for "bash" as a fallback

Thank you,
Roberto Sebastiano