Allow billing group assignment for invited users

Currently when inviting a new user to Miro it is not possible to assign a billing group until the user logs in for the first time (user changes from tab “Invitations” to “Active users”).
Because no billing group can be assigned on invitation admins need to regularly revisit all invited users which have become active to set the correct billing group.

This could be solved by allowing the assignment of a billing group while users are in the “Invited” state.