Snippets nbextension not usable

[diocas]

The snippets extension relies on a file snippets.json that should be manually filled by the user with snippets.
It is located at "/cvmfs/sft.cern.ch/lcg/views/LCG_96python3/x86_64-centos7-gcc8-opt/share/jupyter/nbextensions/snippets" and read-only.

To see if this is configurable. If not, we just install the extension (if still relevant) directly in the docker image.