feat(ui): add _all_ image outputs to gallery (including collections)

[psychedelicious]

Summary

Previously, when a node completed, we checked to see if its output was exactly an ImageOutput. If so, we add the image to the gallery. But there are multiple types of nodes that output images via some other output class. For example, an ImageCollectionOutput. When a node outputted one of these other classes, the UI wouldn't update the gallery. You'd have to refresh the page to see the image in gallery.

With the change in this PR, when a node completes, we check each of its output's properties. If any are an ImageField or list[ImageField], they are all added to the gallery. This covers ImageOutput, ImageCollectionOutput, and all other outputs that have an image.

Related Issues / Discussions

@skunkworxdark mentioned on discord: https://discord.com/channels/1020123559063990373/1049495067846524939/1365019122840371262

QA Instructions

• Existing behaviour should be unchanged (i.e. Canvas outputs should still go to gallery, and single-image-outputting nodes should still go to gallery)
• Nodes that output a collection of images should also go to gallery

Merge Plan

n/a

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

[skunkworxdark]

I tested this against my workflow, which outputs an ImageCollectionOutput, and it works well for me. It also continued to work with a single ImageOutput. However, I have not tried it with other combinations where images are incorporated.