Add DHW data to myheatpump app

[andrekuehne]

I added the ability to add feeds for DHW & DHW target temperature into the myheatpump app.

There is also an added .gitattributes file - I needed to add this to ensure proper cross-platform development on windows devcontainers within VSCode.

[MrTimbones]

I pulled this onto my own instance, and it works well :+1:

My only thought is that maybe this should be toggleable via a checkbox option, like for Flow Rate.

[andrekuehne]

That's a great idea, it won't clutter the interface then. I'll put that in.

[andrekuehne]

I added the checkbox option and it is disabled by default, just like the flow rate. I also applied this to the other PR regarding DHW loss rate calculation