Tigris Moves Async Tasks From FoundationDB to Kafka

Tigris moved asynchronous tasks such as garbage collection off its FoundationDB-based queue and onto Kafka, keeping FoundationDB for tenants, object metadata and replication logs. The custom queue, modeled on Apple's QuiCK paper, caused heavy read and write load competing with user requests plus hard-to-learn bespoke code. Kafka now handles background work while FoundationDB queues remain.