[pixels-retina, index] Implement Upsert Mode for Retina Indexing to Handle Missing Keys

[AntiO2]

Problem Statement: Currently, the Retina and Indexing components follow a strict consistency check. If an UPDATE operation is triggered but the existing key cannot be found in the index, the system throws an error. Similarly, a DELETE operation fails if the key is missing. This strict behavior causes pipeline interruptions when processing out-of-order data or partial snapshots.

Proposed Solution: Introduce a new operational mode for Retina to support more flexible data ingestion (similar to "Upsert" logic).

Update Behavior: If the key is not found during an UPDATE, the system should fallback to an INSERT operation instead of throwing an error.

Delete Behavior: If the key is not found during a DELETE, the system should ignore the request and proceed silently.