Allow adding a dependency with no version constraint

[skykasko]

uv add adds a lower bound version constraint by default. For example, calling uv add requests currently adds the dependency "requests>=2.32.3" to pyproject.toml.

It's possible to have uv use different upper and/or lower bounds, but I could not find a way to add a dependency without any version constraint at all. For example, I want the dependency "requests" added to pyproject.toml without any bounds.

The current default behavior is fine, but I think there should be some way to add an unconstrained dependency, either with a global configuration setting that changes the default behavior, or with a command-line option for uv add.

Apologies if I missed something in the documentation and this is already possible. (Of course I could edit pyproject.toml manually, but it doesn't seem like that should be necessary.)

Thanks for the great work on a fantastic project!