Add record_visibility slot

[mih]

It should have the range Agent to indicate appropriate audiences.

Name and setup are tentative, just need to capture the need.

A dedicated The Public agent instance could function as a ok-to-publish flag.

[mih]

Or it could all the way down in things, and is maybe record_audience with a uriorcurie range... related mapping to dcterms:audience

[mih]

record_dissemination, and make it multivalued: true

[mih]

Yet another approach: With #269 comes the ability to annotate metadata records.

Any given scenario can define a simple tag to approve a record for public dissemination, or whatever other scope.

Which means that this does not have to be solved at the schema level, but can be addressed by a convention established for a particular use case.