Allow changing base path on client side

It is possible today to change the base path for Graph Explorer, but it requires re-building the client side static files. This can be done by passing the `GRAPH_EXP_ENV_ROOT_FOLDER` environment value during the docker build step.

This can be cumbersome, and the desired way to do this would be to set the environment value and have it be applied at runtime. The current static build process will not allow this.

## Proposed Solution

To allow for runtime control over this value, I propose to migrate the root of the app to server side rendering. We use React Router in SPA mode today, but it offers a framework mode that enables server side rendering. This would allow the root layout of the app to be generated at runtime by the server. We could then inject the environment value to the client more easily.