Allow origin to be edited in Portal

[donaldgray]

Raised by customer:

Just noted that it’s no longer possible to change the Origin url when editing records in the portal (this can be useful when wanting to reingest a different file for the same record by changing the origin, or for testing origins)

Not that if we do this we should also implement #888 to ensure the changes are immediately visible and don't rely on hotdisk cache expiring.