Feature Request: Block on unknown licenses

[austimkelly]

Split from: #714

Summary: There's no way to block an unknown license. This would be ideal because you run the risk of introducing copy-left licenses. I'd love a simple flag that blocked on unknown licenses. Additionally, allow-licenses and deny-licenses cannot be used together which is expected behaviour, but there is otherwise no workaround.

Recommendation: Add a new flag with default of false: fail-on-unknown-license.
Docs: When set to true, the action will fail on a pull request if 1 or more licenses have an unknown license. Use allow-dependencies-licenses to specify which packages to omit from the failure when fail-on-unknown-license is set to true.

[jonjanego]

Thank you @austimkelly. We've already got similar feedback that we're tracking in #672 so i'm going to close this issue as a duplicate in order to keep the issue board tidy.