oxipng/jpegoptim the images to losslessly save 10MB total

Would be nice to add this to the workflow for future images, that's a huge reduction.

Converting the existing images(which is not the aim of this PR, it keeps existing formats) to JXL losslessly would save another 20MB, but that conversion has obvious support implications(Alphabet removed support in Chromium, Firefox isn't adding it, only Apple has it).

But hey, if we ignore browsers, doesn't Plasma already support JXL?

At least with JXL one can always convert back.