Enable shared authorship for a single skill

[ottonomy]

Describe the feature request or enhancement you'd like

• As an OSMT admin, I want the ability to have see authors from various organizations display in the author field for instances where those authors have collaborated to develop that RSD.
• The author field should be editable by system admins (and if other lower privilege levels exist, they should not be able to edit the author field)

Describe the problem

• Sometimes skills are developed in partnerships between individuals and organizations. All co-authors want to be represented on the skill definition.

Additional context

• Author data should be presented in the CTDL-formatted JSON as well as the HTML view.
• Database change required, and it would be good to do this in a careful way, the team does not want to have a multi-value data element, they would prefer to normalize author references down to where each value is a single value, and it is not duplicated in the database, but have reference to it. This would enable filtering by skills that reference a particular known author.