[Feature Request] Maximum concurrent executions

[LRagji]

There should be a way by which consumers can be configured with how many maximum batches they can keep in flight(a.k.a not acked)

1. Number can vary from 1 to 100(or x but needs an upper limit)
2. Post reaching the number threshold consumers cannot dequeue any batches until the number reduces or a specified time has reached from last update to the counter as this may indicate unexpected consumer deaths/crash