Include public url of resource in ead / marcxml export
Description
Request from FLVC:
If public interface is enabled resources exported from archivesspace as marcxml or ead should include the public url of the resource in the metadata.
https://www.loc.gov/marc/bibliographic/bd856.html
https://www.loc.gov/ead/EAD3taglib/EAD3.html#attr-instanceurl
