Enhance projects / packages API endpoints to return the effective license

[sschuberth]

Currently, the projects and packages tables for a run's details display only the declared licenses. Instead of adding another column to also display the detected license (once the scanner finished), the idea came up to display the (anyway more important) effective license instead.

In combination with the idea to change the current classic tables layout to rows with card layouts (similar to GitHub issues), this could leave enough room to still display declared / detected licenses per package, e.g. as a sub-row below the package ID (again, similar to the author info in GitHub issues).

While the above mostly talks about the UI, this issue is about implementing the API endpoint to allow for implementing the described UI features.