Migrate v2 AMQP stack to Event Hubs

[conniey]

Dependent on #33708

1. Define the opt-in flag for each Event Hub client types.
2. Update the client builder to have utility type for this opt-in/opt-out (we can copy it from the SB Client builder).
3. Wire the ReactorConnectionCache for Event Hubs.
4. Write the MessageFlux based receiver for the v2 low-level async-receiver.
5. Write the WindowedSubscriber based receiver for the v2 low-level sync-receiver.
6. When doing #_4, #_5 make sure the buffering of the events are predictable (can be computed from prefetch and backpressure const).
7. Reevaluate the operators in the Processor path, remove the duplicate / unnecessary that creates unexpected backpressure to the v2 low level async-receiver.
8. Re-Write the processor pump implementation to make it like the MessagePump we developed in SB.
9. Wire the RequestResponseChannelCache and new ReactorSessionCache.
10. Come up with stress test scenarios – so we can watch for memory, throughput, recoveries.

Tasks

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1. Add configuration options for v2 stack in Event Hubs #40484
   2 of 2
   Client Event Hubs +2
   
2. Wire existing cache classes into Event Hubs library #40499
   3 of 3
   Client Event Hubs +2
   
3. Write MessageFlux for receiving messages in EventHubConsumerAsyncClient #40500
   2 of 2
   Client Event Hubs +2
   
4. Write WindowsSubscriber for receiving messages in EventHubConsumerClient #40501
   2 of 2
   Client Event Hubs +2
   
5. Analyze and if needed rewrite EventProcessorClient partition pump to support v2 stack #40502
   Client Event Hubs +2
   
6. Add stress tests and performance tests for Event Hubs on v2 stack #40503
   Client Event Hubs +2
   
7. Enable existing live tests for V2 Event Hubs #41806
   +0
   

[anuchandy]

Implemented and shipped (5.19.0 with feature-flag, 5.20.0 as default), closing.