[Do not merge] Support both lite and remote kernel

[trungleduc]

References

This is an experiment on adding support for the remote kernels to voici dashboards.

How to test

• Start a jupyter server session with:

jupyter server --ServerApp.token='' --ServerApp.password='' --ServerApp.disable_check_xsrf=True --no-browser --port=8000 --ServerApp.allow_origin="*"

• Build voici dashboard with the following config in jupyter_lite_config.json:

{
  "VoilaConfiguration": {
    "extension_config": {
      "VoiciRemoteKernel": {
        "name-of-notebook-using-remote-kernel.ipynb": {
          "baseUrl": "http://127.0.0.1:8000/",
          "wsUrl": "ws://127.0.0.1:8000/"
        }
      }
    }
  }
}

The notebooks with names in the VoiciRemoteKernel section will use the remote kernel, other notebooks still use lite kernel.

Code changes

Backwards-incompatible changes