Add client locale to RPC READY event

[TheKing-OfTime]

I'm working on a small project that uses Discord Rich Presence among other things. Recently I have received a lot of requests from users for Rich Presence localization to follow the localization of the user's client. However, to my surprise RPC does not allow to get the user locale.

So I request adding locale field to the partial User object that is passed in the READY event.
I think this should not be a problem since the locale can already be obtained via Oauth or Bot Interactions.