Add target_temp_step attribute to water_heater

[LG-ThinQ-Integration]

Proposed change

Add "target_temp_step" attribute to water_heater for customizing temperature step in frontend.

• When the temperature is in Celsius, I want to adjust the target temperature to level 1, but there is no attribute, so it operates at 0.5.
• ha-state-control-water_heater-temperature.ts needs attr_target_temp_step, but water_heater does not have that.

  private get _step() {
    return (
      this.stateObj.attributes.target_temp_step ||
      (this.hass.config.unit_system.temperature === UNIT_F ? 1 : 0.5)
    );
  }

PR: home-assistant/core#135056

[joostlek]

We discussed this architecture proposal and we find that this is indeed a good change to make! So let's continue with implementing this field.

[LG-ThinQ-Integration]

@joostlek
Can I contribute to this issue?

[frenck]

@LG-ThinQ-Integration This is not a feature request forum. You asked for an architectural approval to implement it. It got approved a month ago; we are awaiting your implementation.

[LG-ThinQ-Integration]

merged into dev (home-assistant/core#138920)