Implement entity_category

[TheSimpleZ]

This adds support for entity_category. Now you can separate entities into a diagnostics and config category.
I implemented it in my fork since it allows me to separate all the Error_f* sensors into a diagnostics category for less clutter.
I thought it might be interesting for others.
I hope you don't mind the formatting changes that went along with it. It's VScodes auto-formatting for Python. If you have some auto-formatter that I could run, I wouldn't mind using your style.

Example usage:

- property: Error_f54
    icon: mdi:dishwasher-alert
    hide: true
    entity_category: diagnostic

[oyvindwe]

Thank you very much for your contribution! ❤️

Do you know what "non-primary entity" refers to in the documentation for entity_category?

Good to fix the formatting. I've been thinking of adding black and pylint to the toolchain. Which tool(s)/formatting rules did you use?

[TheSimpleZ]

No worries :)

Unless I'm mistaken, a "non-primary entity" is simply an entity that will not show up in the auto-generated dashboard. But the only reference to it I could find is a random forum post here so I'm not dead certain that's all it does.

It might even be a nice thing to make all unmapped entities a diagnostic entity by default rather than hiding them so they don't clutter up all the mapped ones. If you are fine with such a change, I'd be happy to make a PR for it.

I just used the default rules/settings for the python black formatter extension in vscode.
It comes bundled with the Python extension together with flake8 for linting.