JPEG XL support

It seems that the dataset don't support JXL natively in the same ways as e.g. PNG and JPEG are supported. A JPEG XL is supported by an international ISO standard, gives great compression ratios, finally supports lossless for JPEG and the browser support is now starting to get wide spread (safari has it for some time -> https://caniuse.com/jpegxl, firefox and chrome have it in test mode and publicly stated recently an intention to ship https://groups.google.com/a/mozilla.org/g/dev-platform/c/3YMV4MS34KA?pli=1 and https://groups.google.com/a/chromium.org/g/blink-dev/c/-gDojQbDPRI)

I could find the old PR #5289 which might be the base. But I don't know whether that's sufficient or some more code changes are required to get e.g. the dataset viewer going.

Start by reviewing PR #5289 and the existing PNG and JPEG support paths in the datasets repository. Check whether those paths cover JPEG XL and whether the dataset viewer needs additional changes; done means JXL files work natively in the same ways as PNG and JPEG, including in the viewer.

Written by the indexing model from the issue text.