postFilledWidget parameter feature

[mg3994]

Is your feature request related to a problem? Please describe.
I was Trying to add a small Grey Colored bar at bottom like =>

Column( //like preFilledWidget
      mainAxisAlignment: MainAxisAlignment.end,
      children: [
        Container(
          width: 56,
          height: 3,
          decoration: BoxDecoration(
            color: Colors.grey[100],
            borderRadius: BorderRadius.circular(8),
          ),
        ),
      ],
    )

with the help of submittedPinTheme but , but i doesn't found any method to do so

Describe the solution you'd like
Add a Extra Parameter for postFilledWidget , so that we can align a bar at bottom even after submitted Pin Field / ...many more

Describe alternatives you've considered
or else you can change the Data type of BoxDecoration? decoration, in PinTheme

Additional context
None