Please add the option to pass custom GradientTransform for gradients

[cirediew]

Please add the option to pass our own custom GradientTransform to the track and progress gradient.

For example:

CustomSliderColors(
                  trackColor: Colors.grey,
                  progressBarColors: [Colors.red, Colors.green, Colors.blue],
                  progressTransform: GradientRotation(45 * (pi/180))
                )

This will rotate the progress gradient by 45 degrees.