Add altair to the output components

Would be great to have altair included under https://shiny.posit.co/py/components/#outputs

And have a section about accessing/listening to user interaction, similar to plotly

https://shiny.posit.co/py/components/outputs/plot-plotly/#plots-as-inputs
https://shiny.posit.co/py/docs/jupyter-widgets.html#reactive-read