adding support for gum

[lwiechec]

Summary

Quickly adding plugin for gum.

Checklist

• [x] CI tests are green. If you are using GitHub, you might want to use the plugin_test action from asdf-actions
• [x] asdf-plugins CI sanity checks are green on your PullRequest. Test locally with:

./test_plugin.sh --file plugins/<PLUGIN_FILE>

[lwiechec]

...what might be missing is handling the completions that gum comes with. I wonder if this is something that asdf plugins take care of? and, if so, what would be the best way to implement that, in bin/exec-env?...

[jthegedus]

Handling completions is an area asdf does not have a standard solution for. Exec-env might be the best bet

[jthegedus]

Thanks