feat(NCheckbox): add indeterminate option on checkbox component

[KumJungMin]

🆒 Your use case

• indeterminate is useful on checkbox group.
• for example, checkbox has multiple sub checkboxes.
• we should use to indeterminate to display when any of the sub-checkboxes are checked.

🆕 The solution you'd like

Add Props or Checkbox Group

• please add indeterminate on checkbox component or checkbox group.

Excepted Function

• When you click the indeterminate checkbox, it is either unchecked or checked.
• When in indeterminate mode, checked props are ignored.
• If you create a checkbox group, it must be indeterminate when any of the child checkboxes are checked.

🔍 Alternatives you've considered

No response

ℹ️ Additional info

• indeterminate is established and works many devices and browser versions.
• It’s been available across browsers since January 2020. (mdn docs)
• The indeterminate refers to the state of being neither checked nor unchecked.
• Because it officially provides indeterminate, Developers expect checkboxes to provide indeterminate option.
• So, i suggest indeterminate option on Checkbox component.
• Thank you for read this suggestion. have a nice day :)