Fix undefined id in RadioButtonGroupInput

[johncalvinroberts]

If no id is passed to RadioButtonGroupInput component, the input is given the id undefined_optionvalue. Consider the case where two fields have the same choices, but different source. They will be given the same id, and the form control labels will interfere, which is not nice.

Updated the component to not put undefined_optionvalue into the id of the node, and added a note to the docs.

[djhi]

I think it would be better to generate the id with the source:

`${source}_${get(choice, optionValue)}

It would avoid to explicitly define the id

[johncalvinroberts]

Okay, will do

[johncalvinroberts]

@djhi I replaced with source and removed the ID prop, can still handle backwards compatibility.

If any other changes needed lmk.

[djhi]

Thanks!