Add more granularity to device_class: battery colors

[Mariusthvdb]

Thanks for having the device_class: battery use colors in current Frontend.

It would be even better if we could have some more granularity. Currently the icon remains Green for a very large range. Given the fact many batteries dont gradually die on us, but tend to do so more abruptly, we can be confronted with a still 'green' battery, while it in fact has deteriorated rather significantly.

Before, I was using something like this scale in my setup:

    sensor.*_battery_level:
      templates: &battery_color
        icon_color: >
          if (['unavailable','unknown'].includes(state)) return 'steelblue';
          if (state > 70) return 'green';
          if (state > 50) return 'gold';
          if (state > 30) return 'orange';
          if (state > 10) return 'brown';
          return 'red';

I've moved to the now core coloring, but really miss these levels of accuracy. It just was way more functional, and indicative of the true battery level state of our devices.

Now used in https://github.com/home-assistant/frontend/blob/dev/src/common/entity/color/battery_color.ts are only 70 and 30, so adding to levels for medium-high and very-low would suffice?

Please consider adding?
thanks.

[Mariusthvdb]

please have a look, seems reasonable enough for a small adaptation