Show README and metadata for yanked crates/versions

[Turbo87]

#1058 proposed to reduce information when a crate has all of its versions yanked, but as #1058 (comment) mentions we decided to do something different:

Instead of showing a note that a crate/version is yanked, we should instead show the existing metadata that the backend returns but with a very visible banner (or similar) that this crate/version was yanked by one of the crate owners.

This helps to e.g. figure out who the current owner of a crate is, even when all of the versions are yanked. We currently only display a generic note, without any crate metadata.