Dithering image treatment

eg:

$image->dither([
  'method' => 'floydsteinberg',
  'colors' => ['#fff', '#000'],
]);

Leaving links to the two underlying libraries Kirby uses and which could be used for implementing this:

https://github.com/claviska/SimpleImage?tab=readme-ov-file#maxcolorsmax-dither

https://imagemagick.org/script/command-line-options.php#dither