Add learner_needs field to contentnode API

[rtibbles]

Summary

• Adds learner_needs field to content node API
• Adds response regularization to ensure that older public APIs have their learner_needs field backfilled to [] to ensure a consistent data structure on the frontend
• Handle etag being missing from response headers as an edge case
• Update and add tests for this
• Flyby - fix flakey assertion for files by explicitly sorting.

References

Fixes #12687 Fixes one of the flaky tests remaining in https://github.com/learningequality/kolibri/issues/8255

Reviewer guidance

Does the learner_needs field properly appear in both internal and public API endpoints now? Do the test changes make sense.

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Testing checklist

• [ ] Contributor has fully tested the PR manually
• [ ] If there are any front-end changes, before/after screenshots are included
• [ ] Critical user journeys are covered by Gherkin stories
• [ ] Critical and brittle code paths are covered by unit tests

PR process

• [ ] PR has the correct target branch and milestone
• [ ] PR has 'needs review' or 'work-in-progress' label
• [ ] If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• [ ] If this is an important user-facing change, PR or related issue has a 'changelog' label
• [ ] If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions[bot]]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.18.0.dev0_git.20241029195015.pex
Windows Installer (EXE)	kolibri-0.18.0.dev0+git.20241029195015-windows-setup-unsigned.exe
Debian Package	kolibri_0.18.0.dev0+git.20241029195015-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.18.0.dev0+git.20241029195015.dmg
Android Package (APK)	kolibri-0.18.0.dev0+git.20241029195015-0.1.4-debug.apk
TAR file	kolibri-0.18.0.dev0+git.20241029195015.tar.gz
WHL file	kolibri-0.18.0.dev0+git.20241029195015-py2.py3-none-any.whl

[rtibbles]

I think what you're asking for (the positive case) is covered here: https://github.com/learningequality/kolibri/pull/12763/files#diff-1f9030c267d0588f9d761b21abb8e5f2095df45e6ae7e440d3011cd0d30b2a4aR339

When we run the test suite against the remote endpoint, the same assertions are run, so these assertions are asserting that the learner needs are being properly returned for both the internal and public APIs.