Commit DID operations and publication queues atomically

[Bushstar]

Overview

Gatekeeper previously persisted accepted create and update operations before adding them to mediator publication queues. A queue failure could therefore leave a DID changed locally while the API reported failure and the operation was never published.

This change commits the event, index change, and required publication queue entries within one database operation.

Changes

• Add a required atomic event-and-queue method to the Gatekeeper database adapter contract
• Implement the atomic boundary for JSON, SQLite, Redis, PostgreSQL, and MongoDB
• Preserve normal non-publishing event imports through the existing event method
• Consolidate duplicate legacy Mongo queue documents before enforcing one queue per registry
• Add regression coverage for queue failures, retries, adapter behavior, and Mongo upgrades