Image size adjustments do not preserve image ratio.

The pandoc markdown symtax allows us to adjust the height and width of an image using this syntax:

![text](images/pid_overview.drawio.png){ width=65% }

This has been working fine for us using pandoc --pdf-engine=xetex (or pandoc --pdf-engine=tectonic which I use locally on mobile devices, as well as the default pandoc test.md -o test.pdf). It keeps the aspect ratio of the image. PLB does not do this, and it is cumbersome to do it manually, because the percentage is relative to the page size (or the outer element in html), not to the image height/width. So, this does not keep the ratio:

![text](images/pid_overview.drawio.png){ width=65% height=65% }

In case the latex engine (lualatex?) makes the difference (it might be something else?), maybe we can make the engine customizable?