[Feature request] display complementary value

[amaximus]

I'd like to request a feature for displaying complementary to max value while the bar uses the sensor state value.

Let's take the car oil change as example:

• oil change interval is 20000km => min: 0, max: 20000
• last change was at 40000km (last_change_km)
• now we are at 53000km (current_km)
• the sensor would report current_km-last_change_km

The bar-card (min:0, max: 20000) should display the bar as 53000-40000 (13000; this would be provided by the sensor) while the value displayed should be the complementary to max, 20000-13000 (7000).

So the complementary value to display should be: max - states.sensor.example.state

BTW thanks for this great card.

[Gluwc]

Added in 3.2.0, thanks for the PR!