Support Suspense in cubejs-client-react

It would be very useful for cubejs-client-react to support [suspense for data fetching](https://reactjs.org/docs/concurrent-mode-suspense.html). When building a dashboard, of multiple charts, instead of having to manage the loading of state of each distinct component, suspense allows the parent component to suspend with a loading indicator until all of the promises from children have resolved. This provides a much nicer user experience.