Battery State Display could be customized with parameters

[slgrobotics]

@ottojo It would be nice to have ability to parametrize display look - position, text size, colors etc.

I drafted a solution here:

https://github.com/slgrobotics/ros_battery_monitoring/tree/main/battery_state_rviz_overlay

I can create a pull request, if that's acceptable.

[slgrobotics]

Here is how parameters look in a launch file:

https://github.com/slgrobotics/articubot_one/blob/dev/launch/launch_rviz.launch.py

    rviz_overlay = Node(
        package='battery_state_rviz_overlay',
        executable='battery_state_rviz_overlay',
        namespace=namespace,
        parameters=[{
            'use_sim_time': use_sim_time,
            # see https://github.com/slgrobotics/ros_battery_monitoring/blob/main/battery_state_rviz_overlay/src/battery_state_rviz_overlay_parameters.yaml
            'width' : 450,
            'height' : 10,
            'line_height' : 25,
            'horizontal_distance' : 20,
            'vertical_distance' : 20,
            'font' : 'DejaVu Sans Mono',
            'text_size' : 15.0,
            'horizontal_alignment' : 0,
            'vertical_alignment' : 3,
            'bg_color_a' : 0.1,
            'fg_color_rgba' : '0.0 0.8 0.6 1.0'
        }],
        output='screen',
        remappings=[('battery_state','battery/battery_state')]
    )