Support custom tooltips in the documentation

I was wanting to leverage this for tutorials where I can give a tooltip to a particular set of code I'd like to explain, with perhaps even it pulling up the documentation similar to how to the current tooltip behavior works in argument documentation of classes. (Though just the first is a **great** starting point).

Check out the [Angular docs](https://angularjs.org/) for one example of this (go to the "The Basics" section), Sphynx has a [hoverxref](https://sphinx-hoverxref.readthedocs.io/en/latest/) extension as well :slightly_smiling_face:

This will let the docs + tutorials be even more interactive as instead of having to bounce back and forth between docs users can quickly get either A: what you want to tell them about a particular class or code, or B: It shows the basic docs for that class or function automatically when linked in normal documentation.

Internal slack thread: https://huggingface.slack.com/archives/C02GLJ5S0E9/p1654778861488039