Allow users to manually curate paths to license content for a detected dependency

[jonabc]

This request fills a need similar to additional terms and fully manually curated content.

There is a need to enable licensed users to configure extra license paths within a detected dependency's on-disk content. The specific use case that has come up relates to https://github.com/hashicorp/cronexpr, which is licensed as an OR of AGPLv2 or GPLv3. However licensed doesn't find either file by default because they don't match any of the license file name patterns that are expected. Licensed should be able to account for these scenarios and allow users to manually curate paths to dependency license files when needed.

I'm not sure what the best way to represent these additional license paths in the licensed configuration file structure is, but top of mind there seems to be a few ways to

1. extend the additional terms behavior to support looking for files relative to a dependency's detected folder
2. configure extra dependency license file paths as a use case of manually curating content
3. configure extra dependency license file paths separately from either of the above configuration structures