## Summary
This PR reworks the `upstream_categories` mechanism that is only used
for documentation purposes to make it easier to generate docs using
`all_rules()`. The new implementation also relies on "tribal knowledge"
about rule codes, so it's not the best implementation, but gets us
forward.
Another option would be to change the rule-defining proc macros to allow
configuring an optional `RuleCategory`, but that seems more heavy-handed
and possibly unnecessary in the long run...
Draft since this builds on #5439.
cc @charliermarsh :)
The new `ruff rule` output format introduced in
551b810aeb doesn't print Markdown but
rather some rich text with escape sequences for colors and links,
it's actually the "text" format that prints Markdown, so naming the new
format "markdown" is very confusing. This commit therefore renames it to
"pretty".
This isn't a breaking change since there hasn't been a release yet.
