Add support for Wh

[janneho]

Is your feature request related to a problem? Please describe.
I have a EV charger that reports energy in Wh.

Describe the solution you'd like
Use unit of measurement (kWh or Wh) in calculations. Now integration assumes that energy is in kWh.
Energy panel works fine with Wh.

[martinarva]

I would recommend to make a Wh -> kWh template sensor
`template:

• sensor:
  • name: "Energy Consumption kWh"
    unique_id: "energy_consumption_kwh"
    state: >-
    {% set wh = states('sensor.energy_consumption_wh') | float(0) %}
    {{ (wh / 1000) | round(2) }}
    unit_of_measurement: "kWh"
    state_class: measurement
    device_class: energy
    icon: mdi:lightning-bolt`