## Summary
This adds a `ruff rule --all` switch that prints out a human-readable
Markdown or a machine-readable JSON document of the lint rules known to
Ruff.
I needed a machine-readable document of the rules [for a
project](https://github.com/astral-sh/ruff/discussions/5078), and
figured it could be useful for other people – or tooling! – to be able
to interrogate Ruff about its arcane knowledge.
The JSON output is an array of the same objects printed by `ruff rule
--format=json`.
## Test Plan
I ran `ruff rule --all --format=json`. I think more might be needed, but
maybe a snapshot test is overkill?
d7214e77e6