GitLab

Summary:
This commit re-organizes the tutorials.

1. Put all the tutorials in the left bar and make the section **folded by default**.
2. Add pytorch/tutorials-like cards in index
3. Move feature classifications to a dedicated page.

https://output.circle-artifacts.com/output/job/1f1a04a5-137e-428d-9da4-c46f59eeffa4/artifacts/0/docs/index.html

<img width="1073" alt="Screen Shot 2022-10-28 at 7 34 29 AM" src="https://user-images.githubusercontent.com/855818/198410686-3ef40ad2-c9c9-443c-800e-6e51e1b6a491.png">

Pull Request resolved: https://github.com/pytorch/audio/pull/2767

Reviewed By: carolineechen

Differential Revision: D40627547

Pulled By: mthrok

fbshipit-source-id: 098b825f242e91919126014abdab27852304ae64