Allow the utility_meter to net meter rather than only allow increases.

[JBassett]

Description:

This PR allows utility_meter components to be net metered. My personal use-case is monitoring net power consumption because of solar feeding back to the grid.

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#8631

Example entry for configuration.yaml (if applicable):

utility_meter:
  daily_energy:
    source: sensor.solar_raw_lifetime_net_energy
    cycle: daily
    net_consumption: True
  monthly_energy:
    source: sensor.solar_raw_lifetime_net_energy
    cycle: monthly
    net_consumption: True

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

• Tests have been added to verify that the new code works.

[dgomes]

You should add a test

[dgomes]

I've been thinking maybe the name should be more obvious to users:
"net_comsumption" ?

[JBassett]

I agree that net_consumption would be a better name. I'll change that along with the other comments.

[dgomes]

Looks good

[dgomes]

tks! 🥇