feat(ha): dynamic SoC icon reflects charging state

[nanomad]

Adds icon_template to the SoC MQTT discovery payload so HA renders mdi:battery-charging-{N} when the vehicle is charging and the standard mdi:battery-{N} icons otherwise. Thresholds match HA's native battery device_class icon mapping. Requires HA 2024.x for icon_template support in MQTT sensor discovery.

[danielmsorensen]

@nanomad thanks implementing this change.

I can confirm the icon is now correctly updating based on SoC, however, doesn't seem to be changing based on the charging state.

See the image below which shows the battery is charging, but the SoC icon isn't showing that.

I have copied the template from the PR which does seem to correctly show that the icon should be the charging variant.

So I wonder if the issue is instead with how the charging_entity_id or soc_icon_template is constructed, meaning that it always falls into the else block.