Jupyterlab installation fails on NESH

For jupyterlab from the defaults channel, there seems to be a conflict with the too old glibc available on NESH.

Fix: conda install -n base -c conda-forge jupyterlab nb_conda_kernels

@torge-martin @ilana-schiller-weiss can you check with this modified installation call before I adapt the docs?

Background: The conda-forge channel is often less optimistic about operating-system package versions as it serves a community often stuck with relatively old machines.