Allow `or` combinations in the `allow` list

[julian-klode]

Is your feature request related to a problem? Please describe.

My software project is licensed GPL-2.0-only or GPL-3.0-only, therefore I cannot accept dependencies that use either license, but only the ones that have precisely that or (or a GPL-2.0-or-later).

Describe the solution you'd like
Allow me to specify GPL-2.0-only or GPL-3.0-only in the allow list.

Describe alternatives you've considered
N/A

Additional context
N/A

[Jake-Shadle]

That's just not how the license checking works at all, I'd either have to extend the current allow to additionally take expressions, or add yet another config option specifically for them, either way something that would confuse the config for the vast majority of people who don't need this feature. Considering how specific this is I think it'd be easier for you to just write a script that looks at the output of cargo metadata, I can't imagine there are more than a few crates that even have that exact license expression in the entire crates ecosystem.