After a lot of searching, I now understand that the configuration file in which c.ContentsManager.allow_hidden needs to be set to true is jupyter_notebook_config.py. The suggested jupyter_server_config.py configuration file did not work.
This file, with this exact name, needs to be located under one of the paths presented with the command jupyter --paths. However, this file can also be created at the correct location with the command jupyter notebook --generate-config.
In my case, as I am building environments inside Docker containers using repo2docker, the correct location for configuration files such as jupyter_notebook_config.py is the ~/.jupyter/ folder located at the root directory of the Jupyter project inside each environment.
I initially thought that these configuration files were a single file and that their lines could be entered inside the JupyterHub configuration file located on the host of the Docker containers with the path /opt/tljh/config/jupyterhub_config.d/jupyter_config.py.
Although the issue is now resolved, I do have questions over the difference between the following configurations, because the documentation doesn’t say much:
c.ContentsManager.allow_hidden(insidejupyter_notebook_config.py)c.FileContentsManager.allow_hidden(insidejupyter_notebook_config.py)c.ContentsManager.allow_hidden(insidejupyter_server_config.py)c.FileContentsManager.allow_hidden(insidejupyter_server_config.py)