Ability to set default radio button in Radio component.

**Is your feature request related to a problem? Please describe.**
There is currently no way to set a default radio button in the Radio component. This is because the defaultChecked property of the radio input tag is not exposed as a prop in the component.

**Describe the solution you'd like**
I would like to expose this input tag attribute as a prop in the component so that a default radio button can be set by the developer.