Add sidebar tutorial for chat models

[Rocketknight1]

Draft for now - this PR will add a sidebar tutorial on chat models!

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[Rocketknight1]

This should be ready for review! cc @stevhliu. Also cc @zucchini-nlp and @gante since I'm talking about generation-related topics a lot, let me know if there's anything I'm missing, or if I should be tying this into the existing generate docs better!

[stevhliu]

Very nice and thorough tutorial! There is a lot of info here but I didn't feel like it was too much detail. I think it does a great job of the mental walkthrough and considerations (choosing a model, performance, etc.) you need to make before you even touch any of the code. 👏

[gante]

@Rocketknight1 cool tutorial 🙌