Add a way to do "react native mode" in demo app

[breedx-splk]

See this PR: open-telemetry/opentelemetry-demo#1781

Got me thinking that we could/should have a way to launch the main part of the demo app in a react-native mode. Ideally we would not have to reinvent this or rebuild things, but can use the above mentioned code. Users are often asking about RN, and I think this could be quite helpful.

As I noted in a comment in that PR, there are bound to be some interop challenges and this could help highlight those.