Images in all of Wagtail’s supported formats

[thibaudcolas]

Currently the bakerydemo only contains JPEGs. I’d like to see at least one example of each format Wagtail supports, to simplify testing things like wagtail/wagtail#10781. For formats that are interchangeable with JPEG we can just change existing images. For formats that aren’t (PNG, GIF, SVG), we’d likely need new visuals, or perhaps new content (all keeping on theme).

As well as making our Wagtail core testing easier, I suspect having mismatched formats will also be a more realistic representation of real-world content.

I don’t think this is a must but we could also include:

• Format conversion in image template tags.
• Examples of using images "lossless". Ideally only in a part of the site where this is indeed appropriate for a site (so not on a decorative image)