Enable dark mode viewing on doxygen documentation page

[spuder]

Describe the problem you have/What new integration you would like

esphome should have dark mode

Please describe your use case for this integration and alternatives you've tried:

As a user who frequently works on esphome at night,
I would like the class documentation (doxygen) to include an optional dark mode,
So that my eyes are not stained while looking at class documentation.

Additional context

Enabling darkmode can be enabled by adding an additional css style sheet

https://github.com/MaJerle/doxygen-dark-theme

And then modifying HTML_EXTRA_STYLESHEET