Ability to hide all the completed Epics in board settings.

Right now, in order to hide completed epics from roadmaps, users must individually toggle the 'hide all completed Epic issues' option in the view settings. To improve this process, we suggest adding an option at the board setting level, so that once it is configured by the board administrator, users will not have to repeatedly toggle the 'hide all completed Epic issues' option every time they use the board.