Generalize UNF definition to apply across all Files

[mercecrosas]

We would like to apply a new, more general algorithm to UNF to apply it across all files. See original discussion on this in IQSS/dataverse#2192

Functional Requirements Document (FRD) will be created and linked to this issue.

[leeper]

This seems relatively easy to wrap into the existing UNF standard. Treat a file as a binary vector, base64 encode it, hash using SHA256, and truncate to the specified UNF length. This has could then be aggregated just like dataset UNFs are currently combined to create the study-level UNF.

Even if MD5 is a common standard in archiving, SHA256 seems reasonably widely implemented and would be consistent with the existing UNF standard. I think you would still have to supply MD5's somewhere in Dataverse though, given their prevalence as a checksum.