Allow use webp instead png

[Eduardo-Morales-Alberti]

We are saving bitmap references on our repository, but PNG images have big sizes.
Exists any possibility of using optimized image formats like webp?

[fuhlig]

Very good point.
I'd be very interesting. In my current project VRT is run (on demand) per feature branch for a component library for multiple brands, creating 3000+ screenshots (~300-400mb) per brand.
Achieving a reduction of the usual 20-30% with webp compared to png would be a great improvement on multiple fronts.