Fix security configuration for ROLE_UI_TASKS_CREATE

Steps to reproduce:
See discussion on https://groups.google.com/a/opencast.org/forum/#!topic/users/HlIjx2danDg

Problem:
ROLE_UI_TASKS_CREATE enables Actions->"Start Task". But to make that actually work, the schedule task modal needs to query the list of available workflows.
The current security configuration does however block this since ROLE_UI_TASKS_CREATE is not allowed to access /admin-ng/event/new/processing?tags=archive-ng