New car support docs

This is v2 of [CARS.md](docs/CARS.md). Currently, CARS.md shows all the cars supported by upstream openpilot. The goal of this new page is to be a one stop shop to see the status of any car's support.

It'll include:
* every single car: cars supported in upstream, dashcam cars in upstream, cars supported in forks (even if they're forever in forks), cars we know won't work (no ACC/LKAS), cars with blockers (SecOc), etc.
* super granular columns: has fuzzy fingerprinting, steering torque, etc.
* some info will be populated by openpilot, and the rest will be done manually

This will be super information dense, so I imagine we'll need to move this to a webpage instead of a GitHub Markdown file.

These docs should also help make it clear when a car port is ready to supported and merged into upstream openpilot.

Related:
* commaai/openpilot#27320
* commaai/openpilot#26384

Start by reading docs/CARS.md and the related openpilot issues commaai/openpilot#27320 and #26384. Establish whether the status page should remain Markdown or become a webpage, then define how every listed car category and support detail will be represented. Done means the new page is a one-stop reference for support status and clarifies when a port is ready for upstream support.

Written by the indexing model from the issue text.