Install documentation notebooks with the package #2741
Description
Tim Paine's "jupyterlab-templates" front-end extension provides a means to access notebooks installed with libraries in a read-only fashion.
Such notebooks should be installed in PREFIX/share/jupyter/notebook_templates/LIBRARY_NAME and are picked up by the extension. See e.g. https://github.com/timkpaine/jupyterlab_templates/blob/2660b5f1533d20e59786304dc59dccebf3938882/README.md#templates-for-libraries.
I propose that starting with ipywidgets 8.0, we install all the documentation notebooks in the share/jupyter directory. The notebook_templates name could also be called example_notebooks. As soon as we elect such a path to be the official example notebooks directory, we should do this for other packages as well.
Note: there would be a constraint for such notebooks is that they do not depend on other resources that are local to the notebook path, because they would be open in the current working directory of the notebook user, or we specify in the notebook metadata what ought to be copied alongside the notebooks...