Provide parameter to indicate how a file was imported

There are multiple ways to import files on Nuxeo platform.

For troubleshooting it would be helpful if we knew how a file was imported, i.e., bulk import, aspera, WebUI, direct transfer, sync, etc.

We found Web UI, Direct transfer and Nuxeo drive sharing the same data source as "fileimporter-AssetImporter" in the document data content. We can't tell the difference between different import sources based on it.

Would like to have a parameter in the document JSON that indicates how the file was imported.