feat(checkbox): add required prop (#30157)

Issue number: resolves internal

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

## What is the current behavior?
- Currently, the screen reader do not announce the component as required
when `required={true}`.

## What is the new behavior?
- Added a new `required` prop to be used for accessibility purposes that
adds the `required` attribute to checkbox's inner native input.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!--
  If this introduces a breaking change:
1. Describe the impact and migration path for existing applications
below.
  2. Update the BREAKING.md file with the breaking change.
3. Add "BREAKING CHANGE: [...]" to the commit description when merging.
See
https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#footer
for more information.
-->

packages/vue/src/proxies.ts

@@ -235,6 +235,7 @@ export const IonCheckbox = /*@__PURE__*/ defineContainer<JSX.IonCheckbox, JSX.Io
   'labelPlacement',
   'justify',
   'alignment',
+  'required',
   'ionChange',
   'ionFocus',
   'ionBlur'