Canvas - resolve visibility of orphaned files

[shanbady]

What are the relevant tickets?

Closes https://github.com/mitodl/hq/issues/8516?issue=mitodl%7Chq%7C8519

Description (What does it do?)

This PR includes changes that resolve the visibility in canvas archives according to the following rules:

file is not ingested when:

• If the "files" section in the sidebar is hidden and the file in not embedded on any page
• If the file is marked published but resides in a folder that is hidden or locked and it is also not embedded anywhere

file is ingested when:

• it is explicitly marked as published and parent folder is not locked/hidden and files navbar is visible.
• it is embedded/linked to on a module, assignment, or any html content.

This PR also includes some code cleanup and consolidation of methods into canvas_utils.py

note for reviewer: the majority of the functional changes are in the newly introduced get_published_items method

How can this be tested?

1. checkout this branch
2. ingest course id 14566 (https://canvas.mit.edu/courses/14566) where the "files" in the sidebar is hidden to students ./manage.py backpopulate_canvas_courses --canvas-id 14566
3. note that the only contentfiles for the course are files embedded on assignment pages:

from learning_resources.models import *
LearningResource.objects.get(readable_id__istartswith="14566").runs.first().content_files.all().values_list("source_path")

[mbertrand]

👍