Only ban multiple versions of user-facing dependencies

[epage]

Is your feature request related to a problem? Please describe.
It can be hard to avoid multiple-versions. In particular for dev-dependencies as they tend to sprawl out more than normal/build dependencies (e.g. criterion) yet they are a lower priority. Not many people will care if clap has duplicate depednencies for local development but they will care when depending on clap.

Describe the solution you'd like
Allow configuring multiple-versions = "deny" to only deny when there are multiple within normal/build dependencies

Describe alternatives you've considered

• Allow configuring multiple-versions lint level on per-crate basis #350

Additional context

Granted, this won't help with is-terminal as a normal dependency since it pulls in two different versions of windows-sys.

[jaskij]

Edge case: there are some crates, like build-info which, afaik, need to have the same version as both dependencies and dev-dependencies.