[Feature Request] Support even shapes other than dots to indicate progress.

[agent515]

Journey progress is shown using 'dots' on the screens. You can change the animation, color, and radius but not the shape itself. I'm requesting a feature to support different shapes in one of the two ways:

• Accept custom widgets as selectedIndicator, unselectedIndicator
• Provide a way to select other types of indicators using enum DotIndicatorType (DotIndicatorType.dot, DotIndicatorType.rectangle).

In short, this feature should allow us to create a journey-progress widget as shown below.