Support Tiered Shipping Progress Bar (Multiple Thresholds)

Currently, only one progress bar widget can be active for a single shipping discount campaign. This makes it difficult to represent tiered shipping offers (e.g., free standard shipping over £20 and free express shipping over £40). It would be helpful to support a single progress bar that can display multiple thresholds or tiers within the same widget, allowing merchants to visually guide customers through different shipping milestones in one unified experience.