[User-defined info] Differentiate two packages with 'registry' field

[nockty]

If there are two packages with the same name (from different registries, for instance NPM and PyPi), there is currently no way to differentiate them in the user-defined info file. We should add a way to add the 'registry' field, so that we can have both packages in the .foss.json.

For instance if we add:

{
  "additional-info": [
    {
      "package": "Foo",
      "registry": "PyPi",
      "extra information": "This is a Python package",
      "owner": "John Doe"
    }
  ]
}

It won't affect a package named 'Foo' in the NPM registry (which is the current behavior).