Add containedIn fileProperty to the Extract class

[AdrianUrbanski]

fileSets allow for joining of multiple sources via containedIn property, however it would seem that in recordSets there is no way to extract the specific file the record came from. This would be useful in case of datasets where different splits are contained in separate .zip files, but there is no information about the split in the name of the file.

Is it possible to add containedIn as one of the options for the Extract class?