Feature: show issue assignee on project board (#15232)

* Show assignees in project boards.

options/locale/locale_en-US.ini

@@ -1181,6 +1181,7 @@ projects.board.deletion_desc = "Deleting a project board moves all related issue
 projects.board.color = "Color"
 projects.open = Open
 projects.close = Close
+projects.board.assigned_to = Assigned to
 
 issues.desc = Organize bug reports, tasks and milestones.
 issues.filter_assignees = Filter Assignee