Add UpstreamNonFree.txt to fastlane metadata

This MR is part of addressing #125 (closed). It creates a UpstreamNonFree.txt in the fastlane/metadata/android/en-US/antifeatures directory. This should replace the current disclaimer about this antifeature publish to the fdroiddata repo here, https://gitlab.com/fdroid/fdroiddata/-/blob/master/metadata/ie.equalit.ceno.yml#L2

The addition of this to the fastlane directory of the Ceno repo should allow us to translate it via Weblate. After completing this MR I will merge develop into weblate-integration and attempt to add the translations as they were given in the related issue.