text: Title: support for alternative notebook PDF converters (e.g. webpdf)
  Body: (see #672 and #658 for context)
  
  There are a few engines to convert `.ipynb` to `.pdf`, however, we only support the default one provided by nbconvert, which depends on pandoc and text. It has a few downsides such as not being able to render embedded charts (see #658), we should add support for other engines