feat: Allow passing className props to shadcn custom widgets

[tuanphung2308]

Reason for changes:
Before this PR, className for certain widget was not passed down to shadcn components, leading to form components do not contain classes from ui:className.

Summary of PR:

• Update README.md with picture of the theme!
• Allow passing className props to AddButton, BaseInputTemplate, CheckboxWidget, CheckboxesWidget, RadioWidget, SelectWidget, SubmitButton, TextareaWidget for extra Tailwind customization through ui:className.

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests. I've run npx nx run-many --target=build --exclude=@rjsf/docs && npm run test:update to update snapshots, if needed.
  • I've updated docs if needed
  • I've updated the changelog with a description of the PR
• I'm adding a new feature
  • I've updated the playground with an example use of the feature