Import fail on error fixes

[dbnicholson]

Summary

Make the importcontent --fail-on-error option handle more error cases.

References

Previously this was implemented in #9259 to address #9258. I opened #9590 to track the fixes here.

Reviewer guidance

There are test cases added and #9590 has a procedure to test with local kolibri instances.

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Testing checklist

• [x] 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~~
• [x] 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

• Automated test coverage is satisfactory
• 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