Checkbox.Item: Make the underlying TouchableRipple more configurable

**Is your feature request related to a problem? Please describe.**
I've applied border radius to Checkbox.Item, and it seems to work as expected. However, when the item is `pressedIn`, the underlying touchable ripple doesn't respect the item's border radius.

**Describe the solution you'd like**
Expose an API to tweak the TouchableRipple through rippleStyle or containerStyle.

**Describe alternatives you've considered**
I've considered not using the Checkbox.Item and manually implementing the component with desired level of configuration. But it's a much bigger lift.

**Additional context**

Start at Checkbox.Item and inspect how it creates and configures the underlying TouchableRipple. Define the requested rippleStyle or containerStyle API so the item's border radius is respected while pressed, then verify the behavior with the relevant component tests or examples if available.

Written by the indexing model from the issue text.