The name of the configuration option.
The config value or an empty string if not found.
All values are treated as strings.
For browser based applications, it is assumed that the page HTML
includes a script tag with the id jupyter-config-data containing the
configuration as valid JSON. In order to support the classic Notebook,
we fall back on checking for body data of the given name.
For node applications, it is assumed that the process was launched
with a --jupyter-config-data option pointing to a JSON settings
file.
Get global configuration data for the Jupyter application.