Spike: Remove React peer dependency from addon-docs

[JReinhold]

Objective

Remove react and react-dom as a peer dependency of addon-docs - or alternatively turn into an optional peer dependency.

We want to enable non-React users to use addon-docs without needing to install React themselves and “bloating” their packages. React will no doubt remain in node_modules as a transitive dependency, but that still feels nicer.

Questions we want to answer

• Can we supply a default instance of React with addon-docs, while still allowing React users to use their own instance of React?

👆is important, because React users need to be able to define which version of React they want to use for rendering their components and stories.

[JReinhold]

Closing in favor of moving discussion to #24881