Add labels for custom metadata

[tiran]

Should we add a label system like Kubernetes's labels to Fromager? Labels could be used to provide metadata in package .yaml files. Users can add labels to packages and plugins can act upon the presence and value of a label.

Questions:

• dict[str, str] or dict[str, typing.Any]?
• labels in package settings? or should variants have labels, too?
• global labels in settings.yaml?

Use case:

Declare that a package contains GPU specific code

# torch.yaml`
labels:
    gpu_specific: true

[dhellmann]

I'm not clear how the example you give is useful. What plugin code would look at labels and not already know that a package has GPU-specific code?