Add a group-focus-within variant (and others)

[kripod]

Inspired by tailwindcss-interaction-variants, group-focus-within and other variants should be added to extend the functionality of this project.

[onmax]

I just developed a new plugin very similar to this one that has all Tailwind 3 features.

Check it out here: https://github.com/onmax/tailwindcss-labeled-groups