Add missing reset option for radio field

[gitlabisbetterthangithub]

Should fix getkirby/getkirby.com#2410

Description

This is my attempt at fixing getkirby/getkirby.com#2410. This might not be correct as I might have misunderstood how the field properties table is generated. Hopefully it's correct.

[afbora]

You're right. But AFAIK we also need to unset the reset prop from select field since select field inherit from radio props.

[distantnative]

I am wondering about two things:

• Should a radio button be resettable? The native HTML element isn't.
• If it is resettable, should the default be true - I have doubts as this could be a larger breaking change for setups that have been build with them not been resettable.

[bastianallgeier]

@distantnative I would agree with you here. We don't want them to be resettable in the first place in my opinion.