require ext-imagick

[tacman]

Since we have a hard dependency on imagick, we should require it.

[Spomky]

No, there is no hard dependency. The image processor is optional.

[tacman]

if we implement #84, we can auto-detect imagick and add the

     image_processor: 'pwa.image_processor.imagick'

line if it exists, otherwise we can add a comment there for developers to know how to use it.

On a somewhat related note, the favicon generator library now supports php 8.3