Add traversal_path and dual writes

What does this MR do and why?

Summary

A new field called traversal_path is being added to the AI usage events table in the database. This new field stores a more complete path that includes the organization level (e.g., 1/9/42/), replacing the older namespace_path field which only stored a legacy format without the organization scope. The old field is kept for backwards compatibility but is now considered deprecated. Both new events being written and historical data being backfilled will now include this updated path format. The database is set up so that even older records without the new field can still resolve it automatically at read time using a lookup dictionary.

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Related to #608216