ListWorkerTypes should list only types with accessible workers

Refs https://redmine.teklia.com/issues/8897

The worker types list can be pretty long, and newcomers can get lost. It would be a lot better if the ListWorkerTypes only listed the types where some workers are accessible to the current user.

• admins would get all the woker types as currently
• other users will hit a more complex queryset that lookup Right tables for both group & user access towards type (whatever the level is).