Add support for "Powerfox flow" gas meter

[koelben]

Describe the integration you'd like

I'd like to have the "powerfox FLOW" gas meter to be integrated.

What are your use cases for this integration?

I want to monitor my gas consumption within the energy dashboard.

Is there a public API or documentation?

https://support.powerfox.energy/hc/de/article_attachments/35700057681425

Anything else?

There already exists an integration for other devices of the same manufacturer
https://www.home-assistant.io/integrations/powerfox

• thanks to @klaasnicolaas, but for the gas meter no integration is available at the moment.

[klaasnicolaas]

First steps to integrate the Powerfox FLOW: home-assistant/core#158196

./Klaas