Provide a slot for QOptionGroup to customise the label content

[dsl101]

Is your feature request related to a problem? Please describe.
I have some individual checkboxes using this kind of layout:

<q-checkbox v-model="model" label="Setting X">
  <q-item-label caption>Explanation of what setting X is for</q-item-label>
</q-checkbox>

I'd like to use QOptionGroup for some of those settings, but can't follow that style, as there is no 'sublabel' prop, nor a scope to customise the label element of that component.

Describe the solution you'd like
Something like:

<q-option-group v-model="model" :options="options">
  <template #label="prop">
    <q-item-label>{{prop.node.label}}</q-item-label>
    <q-item-label caption>{{prop.node.explanation}}</q-item-label>
  </template>
</q-option-group>

Describe alternatives you've considered
Individual QRadios with external code to handle the group / clearing / maintaining model, etc. but that's kind of what QOptionGroup is for I think.

[rstoenescu]

Will be available in Quasar v2.2.0