Timed unhiding/release of regular assignments

[donny-wong]

For normal assignments, we have to manually change the “Hide assignment from students” from “Hidden” to “Visible” when we want to release it to students. However, instructors often want to specify a time to do this automatically. For example, “Release the assignment at [a specific time]”, e.g. for the weekly preps in 148.

Timed Assessments have an option where files/etc. are withheld until the start time. It would be good if something similar were implemented for normal assignments. e.g. "Unhide at [date and time]" option.

[donny-wong]

closing issue as it is a duplicate of #6752