Project Builder: add Field Guide Cleaner (admin-only)

[shaunanoordin]

PR Overview

Supports #7405
Affects: Project Builder -> Edit Field Guide page (Admin mode only)
Staging branch URL: https://pr-7406.pfe-preview.zooniverse.org/lab/2023/guide?env=staging or https://pr-7406.pfe-preview.zooniverse.org/lab/24617/guide?env=production

This PR adds an admin-only tool, the Field Guide Cleaner, to the edit Field Guide page.

• As noted in 7405, there's a bug in the Edit Field Guide page that lets "cleared" icons sometimes still stick around as part of a Field Guide's attached_images.
• This tool lists all images (icons) attached to a Field Guide, and shows which of those images are actually used in the Field Guide, and which are orphans.
• There's also a button that deletes (attached_image_resource.delete()) those orphaned icons.
• To enable this tool, ** you must have admin mode enabled.**

⚠️ NOTE: this tool assumes that attached_images uploaded for a Field Guide aren't used anywhere else. This is a pretty safe assumption given the use case, and given that the uploaded icons are supposed to be deleted when their associated FG pages are deleted, but theoretically it's possible to do some really weird linkages with the Panoptes API if you're a mad scientist or something.

Status

Ready for review.

I'm going ahead and running this for Marine Lens: Florida Keys to help solve their immediate issue.

[coveralls]

coverage: 55.977% (-0.01%) from 55.991%
when pulling fc52cf3 on fix-too-many-field-guide-images
into cfa8aab on main.