Add GitHub codespaces as an alternative to Binder

[pavithraes]

We have a link to Binder in our README for folks to quickly setup and run the tutorial. With the recent instability of Binder due to lack of funds, should we consider adding GitHub's codespaces as an alternative?

I noticed xarray do this: https://github.com/xarray-contrib/xarray-tutorial#github-codespaces, and looked into it. It's quite straightforward to add. It's also a safe+viable option for Bokeh because we don't have any tricky dependencies like extensions or distributed compute.

[bryevdv]

I missed this issue until now, this seems like a very good idea