Design the GraphQL API needed to show all users involved in a campaign

Created by: mrnugget

As just discussed, we need a way to show:

• Creator of the campaign spec
• The initial applier of a campaign
• The last applier of a campaign
• When the last applier applied the campaign spec

We also need to remove the author field on Campaigns since campaign don't have an author anymore.

Post the proposed API design in this ticket.