Update lint documentation to use markdown headlines
This PR updates all lint documentation to use markdown headlines. It additionally removed the *Known problems* section for lints without any problems. I've double-checked all automatic replacements, but a second pair of eyes is definitely appreciated!
I wasn't sure when you wanted to switch to the new metadata collection tomorrow, I therefore prepared this PR today. And that's it this is a standalone PR to keep the other related PRs reviewable.
changelog: none
r? `@flip1995`
cc: #7172
Note: This should be merged with the other metadata collection related PRs.
464c85c8c1