Add sphinxcontrib-drawio

[BrentK-ADI]

Add support for draw.io drawings directly, versus needing to export to an image file.

[gastmaier]

Hi! is there any issue with the sphinxcontrib.drawio enabled with doctools?
In general, you can add third-party extensions to the list on extensions at conf.py

I only discourage using extensions that render content on the client side using JavaScript, like wavedrom, because it:

• requires fetching third-party scripts (most of the times).
• makes exporting to other formats (like pdf) harder, because you have to patch and replace with another solution.

I see that https://pypi.org/project/sphinxcontrib-drawio/ calls drawio executable (JavaScript + Electron) (https://github.com/jgraph/drawio), so make sure to set up the environment during the CI also.