Run Licensee on payload for license files

A lot of NuGets like this one: https://www.nuget.org/packages/NuGet.Client/3.4.3 have a license file like this: https://raw.githubusercontent.com/NuGet/NuGet.Client/dev/LICENSE.txt

but we're stating that they're NOASSERTION. We could go grovel through release dates, look for the commit with the license file it, and then run Licensee on the payload of that file to see if we can get the license data out of there.

@dabutvin