Converting python plugin-in shellout.py from gimp 2.x to 3.x

[iiey]

Hi nchen,

I didn't think much about Radio Option because your advice with add_choice_argument() fits for that case too.
   

The Gimp.message() together with try/except and inspection the Error Console (Add Tab > Error Console) help a lot by debugging, thank you very much again! ?

Now the plugin is working again, at least it works for me locally with win11 and gimp3 ?
I put it in a repository here for archive: https://github.com/iiey/nikGimp

Any advice and/or PRs are welcome!