Potential documentation topic for metadata: understanding globally unique ID

[pvangay]

Champions reported during beta testing the Submission Portal that they were unsure of what values could go into this field. They were unfamiliar with UUIDs and IGSNs. They had a Biosample Accession for their sample but that didn't seem valid for this field.

We should provide better documentation to walk users how to fill this out. Also, I can't recall if we'll ever mint our own IDs... but would be good to address that too.

FYI @mslarae13