Run minimal version tests against *all* crates that are scheduled to be published

[suzmue]

This could be a part of the CI, or can be done as part of the release. But it probably should be done.

Something like:

$ cargo run -p minimal-version-helper prepare
$ cargo workspaces plan --skip-published | xargs -I PKG cargo minimal-versions check -p PKG

This should also be run with all features enabled most likely.