Kanban colored boards (#16647)

Add a column Color in ProjectBoard and color picker in new / edit project board form.

services/forms/repo_form.go

@@ -499,6 +499,7 @@ type UserCreateProjectForm struct {
 type EditProjectBoardForm struct {
 	Title   string `binding:"Required;MaxSize(100)"`
 	Sorting int8
+	Color   string `binding:"MaxSize(7)"`
 }
 
 //    _____  .__.__                   __