Source workspace name from `workspace.metadata.name`

[dpc]

The problem with workspace.package.name is that unlike workspace.package.version nothing really needs to inherit it, as packages usually have more specific names.

So when setting it just so crane can pick up workspace build "name" one will keep getting:

warning: /home/dpc/lab/fedimint/Cargo.toml: unused manifest key: workspace.package.name

on every cargo command.

Would be nice if crane could fallback to workspace.metadata.name if workspace.package.name is not available which cargo doesn't mind being unused.