Restore UI to set "default schedule media-source"

Parent: [EPIC] Complete Calendar Experience (aura#255 - closed)

The "default schedule playlist id" UI which was part of the "schedule detail dialog" in the calendar view got removed during dashboard refactoring and should be restored.

The relevant Steering permission is already provided by steering#234 (closed).

Proposal

• Instead of pressing it into the current modal dialog in the calendar view with limited space, add it to the schedule detail view as a follow-up task of #243 (closed).

Blocked-by

• [STORY] as a ProKo, I want to manage schedules ... (#243 - closed)