group task background with low opacity

[EngPetit]

I would like to propose to add the color associated to the group in the background of the group' task :
example :

the code is simple :

add this code to the draw function of group class:

painter.draw_box(
            self.box_x+self.box_width+painter.gap_between_group_box_and_timeline,
            self.box_y,
        (painter.width
            - (painter.left_margin + painter.right_margin)
            - painter.gap_between_group_box_and_timeline
        ) * painter.timeline_width_percentage,
            self.box_height,
            self.fill_colour+"20", #20 percent of opacity
        )

and split the group and the task draw function:

  def draw_group_task(self, painter: Painter) -> None:
       #painter.width-self.box_width-(painter.left_margin + painter.right_margin)-painter.gap_between_group_box_and_timeline,
       # Step 2: draw tasks
       for tasks in self.tasks:
           tasks.draw(painter)

we need to split group draw function to maintain the vertical line on the group background:

        ### Draw the roadmap groups
        for group in self._groups:
            group.draw(self._painter)

        ### Draw timeline vertical lines on the roadmap
        self._timeline.draw_vertical_lines(self._painter)
        
        ### Draw the roadmap groups task
        for group in self._groups:
            group.draw_group_task(self._painter)