On team page, add a separate category for volunteers

[hollomancer]

Feature

Why is this feature being added?

For legal and financial reasons, we need a third category for volunteers outside of the staff. Need a third category on the team page for this.

What should your feature do?

• In the API under Team Members, create a 'volunteers' group.
• Have a corresponding frontend experience to display volunteers.

[kylemh]

@hollomancer

In the API under Team Members, create a 'volunteers' group.

Requires a back-end ticket, and this ticket will be blocked until it's complete.

[kylemh]

Documented here: https://github.com/OperationCode/front-end/issues/173

Still requires a back-end issue @dmarchante