"Run in webcenter links" directly from the docs notebooks page

[daquinteroflex]

This is both a bug and a feature request. The bug I will fix in a linked PR and the feature, unfortunately is a bit more involved and will take longer - so I've created this issue.

The google collab link doesn't work due to executablebooks/sphinx-book-theme#679

I tried to configure it on these lines but it's tricky in our case. https://sphinx-book-theme.readthedocs.io/en/stable/content/launch.html
I will temporarily remove it for now.

However, it'd be nice if we can add a notebook to run in the webcenter at least for now. See executablebooks/sphinx-book-theme#462