Allow endpoints to dispatch tasks without authN
The pulp_ansible plugin is failing because it has an endpoint that dispatches a task without a logged in user.
Skip permissions assignment when there is no user
pulpcore.plugin.models.AutoAddObjPermsMixin.add_for_object_creatorto skip assignment of permissions if there is no known user. This allows endpoints that do not use authorization but still create objects in the DB to execute without error.