Create a new route/function to allow mass emailing of team members.
The backend needs to have a new API route for mass emailing of users by project admins.
This needs to check that the user_ids are indeed members of the project, and that the current user is an admin.
The API route should be /api/objet_type/:id/send_emails
where object type can be a project, a challenge, a program or a community.