CI: Use Netlify for notebooks tests

[ViktorvdValk]

Update the CI for notebook tests to use Netlify and Nbmake. A NETLIFY_TOKEN and a NETLIFY_SITE_API_ID still have to be added to the secrets of the ITKElastix repo. I suppose this it's better to make an account from within ITK for this and use that or shall I add my token and api_id to the ITKElastix secrets?

[thewtex]

@ViktorvdValk great work!

Yes, we have an account for the Insight Software Consortium. I set up NETLIFY_TOKEN and a NETLIFY_SITE_API_ID for https://itkelastix.netlify.app .