Support max-pixels attribute for image upload

[lognaturel]

User-facing docs
spec

In Collect, the scale down happens when the image is captured.

[garethbowen]

Using https://www.npmjs.com/package/image-blob-reduce adds 50kb or 20kb gzipped.

[latin-panda]

Hey @garethbowen, have you looked at browser-image-compression? It feels like a more modern JS approach and still light (19.2kB gzipped). I like that it's zero-dependency (no Pica), however, I haven't seen a comparison of image quality under the same conditions.

[garethbowen]

@latin-panda Thanks for that. It seems strange but both libraries make it difficult to set the quality. Our docs suggest we use 0.8 quality so I'd like to set that if possible. The browser-image-compression one allows passing a max MB size, and then it keeps lowering the quality in a loop until the file size comes in under that limit. This seems like a bad performance hack but also not the metric we're targeting.