This PR fixes some issues with the new BatchQueue by implementing the
full two-phase dequeue process in the FairQueue, and moving the
responsibility of consuming the worker queue to the BatchQueue and
independently enabling it via the `BATCH_QUEUE_WORKER_QUEUE_ENABLED` env
var. We've also introduced the `BATCH_QUEUE_SHARD_COUNT` env var to
control the count of master queue shards in the FairQueue. We can also
control how many queues are considered in each iteration of the master
queue consumer via the `BATCH_QUEUE_MASTER_QUEUE_LIMIT` env var.
This PR will also now skip trying to dequeue from tenants that are at
concurrency capacity, which should lead to fewer issues with low
concurrency tenants blocking higher concurrency tenants from processing.
Eric Allam
062766e974