The url for the request.
The initialization options for the request.
The server settings to apply to the request.
a Promise that resolves with the response.
If the url of the request is not a notebook server url.
The url must start with settings.baseUrl. The init settings are
merged with settings.init, with init taking precedence.
The headers in the two objects are not merged.
If there is no body data, we set the content type to application/json
because it is required by the Notebook server.
Make an request to the notebook server.