Convert management command to address licensing metadata issues

[bjester]

Summary

Converts the management command that was previously used to export data for analyzing the issue of incomplete licensing metadata for nodes that have missing source nodes that were in public channels.

• Uses a CSV for applying licensing metadata on a per-channel basis, all for public channels
• Limits usage of .iterator() to when it handles a channel with imported nodes, to reduce the duration of how long a transaction is open

References

• The 'Copyright holder' field for a synced resource is marked as required but it's not editable #5683

Reviewer guidance

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AI usage

• Changes to the management command were implemented, then AI was instructed to create tests for LicensingFixesLookup. Those tests were refactored to be more robust, then AI was told to update the management command tests for the same scenarios. Corrections were made to thoses tests until they passed.