fix(NcActionRadio): change modelValue to behave like NcCheckboxRadioSwitch

[Antreesy]

☑️ Resolves

• v-model: Boolean is quite unusable for radio-buttons, as it should store selected value (one from many options)
• Should be changed by developers when migrate from checked to v-model, apart from that works as before

🖼️ Screenshots

🏚️ Before	🏡 After

🚧 Tasks

• check if it's a breaking change
  • this.model = this.$refs.radio.checked is kept for backward compatibility

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 3️⃣ Backport to next requested with a Vue 3 upgrade

[susnux]

Makes sense from my point of view and probably makes usage simpler

[Antreesy]

/backport to next