Configure site builds to fail on error

[maximlt]

Currently building a site with NBSite doesn't fail if an error occurs while running a notebook. There should be an option to configure the build to fail in such case. Ideally, it would not fail as soon as an error occurs but keep running all the notebooks, and only then reports the failures.

When this functionality is found/implemented, we would enable it over the different projects. This would need to be done incrementally as it's likely some of the current site builds would immediately fail. We'd need to decide whether enabling this during a release is a good idea or not. I'd suggest that this should be enabled on all the scheduled runs though.