Only allow users in admin group to delete composes
    
    Currently only ALLOWED_GROUPS can create and delete composes, however we
    may want to grant the creating and deleting permissions to different
    groups of users, so add ADMIN_GROUPS to only allow users in such groups
    to delete composes.
    
    Since we don't manage groups in odcs db, to grant a user with delete
    permission, the user must be added to a (or some) particular group(s)
    in the backend auth system first, and then add the group(s) to
    ADMIN_GROUPS in config.