Allow use of identifiers in creator provenance metadata

[micheldumontier]

for Metadata, i see that created_by links to a string - it would be great if we can (optionally?) have a agent description that can be linked to known identifiers (e.g. orcid)

[pnrobinson]

@julesjacobsen I think that given the variety of ways of denoting identifiers, this is a project-specific task that could be implemented by using a regex in the project-specific JSON schema validation file?