Add package 'alias' to allow multiple packages with the same pubspec package name

[josh-burton]

In my project I use Melos mainly to run scripts across all packages in my repo, rather than managing dependencies between packages.

I have multiple packages that all have the same package name (so I can swap out behaviour but have my app reference the same package).

Melos currently fails with this use case as it doesn't allow packages with the same package name.

Could Melos support an alias in the pubspec file to allow this?