Add a description field to people in the email registry

It would be great to allow an optional description field for things like the person's position like "Dean" or "rector" for people in the administration, to achieve a similar effect as linking teachers to their channels.

This would be useful since it's not immediately obvious what role an administration member has (as it is with teachers), and it would be easier to search administration members by their position rather than their name (esp. if the user doesn't know the name of the person with the position in question)

The issue does not name files, tests, or entry points. Start by locating the email registry's person model, storage, display, and search handling, then trace how teacher channel links are represented. Done means an optional position or description can be stored, shown for administration members, and used when searching by that description.

Written by the indexing model from the issue text.