docs: CARS.md 2.0

[jyoung8607]

Resolves #1144 by introducing other_cars.py, allowing us to generate CarDocs for cars outside of openpilot. This is WIP and still a bit trash, but illustrative enough to start the bikeshedding.

Direct links to view the work in progress

• CarDocs for community supported and incompatible cars, other_cars.py
• New generated CARS.md

TODO

• [ ] Move generation to opendbc, but save output in openpilot (?)
  • [ ] Unwind development-only move of CARS.md and assets just before shipping
• [ ] Verify this doesn't hurt any comma.ai/vehicles or shop.comma.ai flows
• [ ] Make other-than-official cars much more visually obvious (background color, italics, ?)
• [ ] Cleanup/revamp the template text in accordance with the New Way of Things
• [ ] Remove placeholder "dashcam mode" support logic, replace with the actual reason they're in dashcam mode
• [ ] Out-of-tree cars should show N/A for other characteristics
• [x] Some complex footnotes should become intra-document #links
• [ ] Internal discussion about links to forks
• [ ] Resolve other TODOs
• [ ] Cleanup
• [ ] Tests for new support type logic