Added subDisplayKey option

[ialmoqren]

To make it easier to use localized arrays

[renrizzolo]

nice, thanks for this.
I'm thinking it might make more sense for the prop to be a function that receives the item and is expected to return a string, so the translation could be retrieved from elsewhere (for example).
{subDisplayKey ? subDisplayKey(item) : item[displayKey]}

I guess it would need to be called something more appropriate like customLabelRender though.

[github-actions]

This PR is stale because it has been open 45 days with no activity.