Enable tab completion for `ruff rule` (#7560)
## Summary
Writing `ruff rule E1`, then tab, shows:
<img width="724" alt="Screen Shot 2023-09-20 at 9 29 09 PM"
src="https://github.com/astral-sh/ruff/assets/1309177/00297f24-8828-4485-a00e-6af1ab4e7875">
Closes https://github.com/astral-sh/ruff/issues/2812.
