Auto-generate docs for telemetry events

[minrk]

It would be pretty handy if the sphinx docs automatically generated content from the jupyter-telemetry event schemas.

Maybe this should even be implemented as a sphinx extension provided by jupyter-telemetry so that any project adopting telemetry could get event docs?

cc @yuvipanda @Zsailer @willingc

[Zsailer]

Totally agree. I've got something basic working in the notebook telemetry PR here. I think you're right, we should make this a sphinx extension.

I'll on this soon and ping here when it's finished.