Use RestartTask to restart a task

https://redmine.teklia.com/issues/6515

The Restart task button must now be available to anyone with an admin access to the process' corpus, and not just to instance admins. Instead of calling PartialUpdateTask to set the state to pending, it should now call the new RestartTask endpoint. The task returned by this endpoint should be included in the process in the store so that it is immediately visible in the graph.