allow forcing tanka use or provide just-in-time detection.

[jemag]

Currently tanka use is conditional to checking tk tool jpath. However this check is done on setup. This means that if the neovim instance is first opening a file where this is invalid, any further JsonnetEval where tanka is required won't work.

For example
/home/jemag/Projects/kubernetes-platform-poc is not valid jpath
/home/jemag/Projects/kubernetes-platform-poc/tanka is valid jpath

If opening a file in /home/jemag/Projects/kubernetes-platform-poc first, then going into a file in /tanka will still call jsonnet instead of properly calling tanka.

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Potential solutions:

• Allow forcing the use of tanka through a config option within setup
• Check jpath not on setup but perhaps on autocmd such as BufEnter.