Alert user when the queryClient is configured in a way that it is shared between different users and requests

[josephfarina]

Hello!

We recently just ran across a bug that was very difficult to track down. It was caused partially by initializing queryClient outside of our app — which caused the data to be shared between requests and users.

I noticed that that at one point the Next.js example initialized the queryClient this way and is the reason we did so (and I assume other people may have as well): 862bb2b

I think it could be really valuable to other users to alert them that their queryClient is misconfigured via a console.warn!

[TkDodo]

not sure how we would find that out? In a client rendered app, it is advised to create the client outside of the App component to have a stable reference. useState can also be used, but I wouldn't know under which condition we should issue the log statement...