Add --metadata option to display metadata about input images.

https://www.reddit.com/r/rust/comments/d4inkc/imagecli_a_pure_rust_image_processing_command/f0d07h0?utm_source=share&utm_medium=web2x

https://imagemagick.org/script/identify.php

When [this image library PR](https://github.com/image-rs/image/pull/1014)  lands we can implement a basic version of this feature.