Add unused-ignore-comment rule

[MichaReiser]

Summary

This PR implements a new Red Knot rule that reports unused type: ignore or knot: ignore[code] comments.

The tricky part about this rule is that unused-ignore-comment can itself be suppressed by using an ignore comment.
Ruff only supports suppressing unused-noqa warnings with a file-level noqa comment. Unfortunately, we
don't support file-level ignore comments other than type: ignore but we also want to warn about unused
file-level type: ignore comments.

That's why this PR proposes that we allow suppressing unused-ignore-comment but only by using knot: ignore[unused-ignore-comment].

Open questions

Ruff calls the rule unused-noqa, but I'm not sure if unnecessary or useless would be more fitting because you can't use an ignore code. But an ignore code can be useless (or unnecessary).

Test Plan

Added mdtests

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.