add support for AVIF image format

[milahu]

currently AVIF images are not supported

$ chandra test.avif test.avif.html 
Error: Invalid value: Unsupported file type: .avif

also piping a PNG image to stdin does not work

$ magick test.avif png:- | chandra - test.avif.html
Error: Invalid value for 'INPUT_PATH': Path '-' does not exist.

$ magick test.avif png:- | chandra /dev/stdin test.avif.html
Error: Invalid value for 'INPUT_PATH': Path '/dev/stdin' does not exist.

also piping a PNG image through a named pipe does not work

$ chandra <(magick test.avif png:-) test.avif.html
Error: Invalid value for 'INPUT_PATH': Path '/dev/fd/63'' does not exist.

workaround
create a temporary PNG image file

magick test.avif test.avif.png
chandra test.avif.png test.avif.html