add partner contact info

[mtorres253]

In most cases when we work with agency partners, there is a main contact there in addition to the 18F contact. This creates some difficulty for comms because there is currently nowhere in the schema to store this information. We should have such an attribute

Acceptance criteria: When I am creating a data-private entry or about.yml entry for a project And I have a partner contact I should be able to enter this information in the schema And it should be available via the Team API

Notes: We will want to do more research with external audiences to build out Team API to meet their needs. We will want to research the information we make available about partners in general