Port numpyro.render_model() to Pyro

[fritzo]

Resolves #2957

This ports numpyro.render_model() nearly verbatim to pyro.render_model(), including the tutorial.

I've prioritized this because of a recent user story: a scientist wanted to learn Pyro/NumPyro, and eventually chose NumPyro because the learning curve was less steep. This scientist said:

numpyro.render_model() was very helpful! It felt almost like numpyro is a probabilistic model rendering library that happened to also perform inference. I couldn't figure out what this numpyro.plate thing was until I could play around with models and see how their plate structured worked visually.

Ported functions and files:

• get_model_relations() is simpler than in numpyro, due to @ordabayevy's ProvenanceTensor Support discrete variables in get_dependencies() via ProvenanceTensor #2959
• generate_graph_specification() is copied nearly verbatim
• render_graph is copied nearly verbatim
• render_model is copied nearly verbatim
• model_rendering.ipynb is copied nearly verbatim

Tested

• tutorial is added to test harness
• checked rendering and doc links manually

[fehiepsi]

Looks great to me! The provenance one is nice.

[fehiepsi]

typo: lists -> list

[fritzo]

done, thanks for catching!