Read Consistency with Database Replicas - Shopify

Introduces a solution for monotonic read consistency in database replicas by modifying ProxySQL. This involves using a `consistent_read_id` in query comments to hash and deterministically select a replica for a series of related reads, ensuring a coherent data timeline. Addresses two key issues: handling server unavailability by indexing into the full list of configured servers and then disqualifying unavailable ones, and disabling ProxySQL's secondary load balancing for consistent read requests to prevent overriding the hash-based selection.