Build IJulia notebook for each doc example

[kbarros]

Each example in the docs should contain a link to a corresponding IJulia notebook. The latter should be automatically built in our "build docs" Github action.

Relative to the markdown docs, IJulia notebooks should:

• Use WGLMakie if in IJulia environment
• Have appropriate default resolution
• Have the correct shade of gray for spins (perhaps this WGLMakie bug could be fixed?)
• Have appropriate size of axis labels (this might get easier with Makie 0.20)
• Generate the correct HTML for image links

Also, as part of the refresh, we should deal with #hide pragmas so that notebooks are fully executable.

[kbarros]

I started working on it, but the feature might depend on issues in other packages, e.g.:
MakieOrg/Makie.jl#3184
fredrikekre/Literate.jl#222

[Lazersmoke]

If Literate can target IJulia, then surely it handles the hide tags correctly?